Update nitrokey crate to 0.4.0-alpha.2

This change updates the dependency to nitrokey to version 0.4.0-alpha.2.
In addition to minor interface changes for the get_*_firmware_version
and get_*_retry_count functions, several functions that change the
device state now require a mutable handle to the nitrokey. Hence, this
patch a number of function signatures to accept mutable device objects.

Import subrepo nitrokey/:nitrokey at 34efcfadf1436102e42144f710edabaa2c4b55cd

15 files changed, 525 insertions, 350 deletions

diff --git a/nitrokey/.builds/archlinux-use-system-lib.yaml b/nitrokey/.builds/archlinux-use-system-lib.yml
index ac0fc0f..ac0fc0f 100644
--- a/nitrokey/.builds/archlinux-use-system-lib.yaml
+++ b/nitrokey/.builds/archlinux-use-system-lib.yml
diff --git a/nitrokey/CHANGELOG.md b/nitrokey/CHANGELOG.md
index 24c79af..e98e857 100644
--- a/nitrokey/CHANGELOG.md
+++ b/nitrokey/CHANGELOG.md
@@ -31,6 +31,13 @@ SPDX-License-Identifier: MIT
   - Return `Error::Utf8Error` if libnitrokey returns an invalid UTF-8 string.
 - Implement `From<(T: Device, Error)>` for `Error`.
 - Fix timing issues with the `totp_no_pin` and `totp_pin` test cases.
+- Always return a `Result` in functions that communicate with a device.
+- Combine `get_{major,minor}_firmware_version` into `get_firmware_version`.
+- Add `set_encrypted_volume_mode` to `Storage`.
+- Use mutability to represent changes to the device status:
+  - Implement `DerefMut` for `User<T>` and `Admin<T>`.
+  - Add `device_mut` method to `DeviceWrapper`.
+  - Require a mutable `Device` reference if a method changes the device state.
 
 # v0.3.4 (2019-01-20)
 - Fix authentication methods that assumed that `char` is signed.
diff --git a/nitrokey/Cargo.toml b/nitrokey/Cargo.toml
index 084bcea..fd6fef7 100644
--- a/nitrokey/Cargo.toml
+++ b/nitrokey/Cargo.toml
@@ -3,7 +3,7 @@
 
 [package]
 name = "nitrokey"
-version = "0.4.0-alpha.0"
+version = "0.4.0-alpha.2"
 authors = ["Robin Krahl <robin.krahl@ireas.org>"]
 edition = "2018"
 homepage = "https://code.ireas.org/nitrokey-rs/"
@@ -14,12 +14,13 @@ keywords = ["nitrokey", "otp"]
 categories = ["api-bindings"]
 readme = "README.md"
 license = "MIT"
+exclude = [".builds/*"]
 
 [dependencies]
 libc = "0.2"
-nitrokey-sys = "3.4"
+nitrokey-sys = "~3.4"
 rand_core = {version = "0.3", default-features = false, features = ["std"] }
 rand_os = {version = "0.1"}
 
 [dev-dependencies]
-nitrokey-test = {version = "0.2"}
+nitrokey-test = {version = "=0.2.0"}
diff --git a/nitrokey/README.md b/nitrokey/README.md
index 069fed1..8c596eb 100644
--- a/nitrokey/README.md
+++ b/nitrokey/README.md
@@ -38,8 +38,7 @@ supported by `nitrokey-rs`:
 - `NK_is_AES_supported`.  This method is no longer needed for Nitrokey devices
   with a recent firmware version.
 - `NK_set_unencrypted_volume_rorw_pin_type_user`,
-  `NK_set_unencrypted_read_only`, `NK_set_unencrypted_read_write`,
-  `NK_set_encrypted_read_only` and `NK_set_encrypted_read_write`.  These
+  `NK_set_unencrypted_read_only`, `NK_set_unencrypted_read_write`.  These
   methods are only relevant for older firmware versions (pre-v0.51).  As the
   Nitrokey Storage firmware can be updated easily, we do not support these
   outdated versions.
diff --git a/nitrokey/src/auth.rs b/nitrokey/src/auth.rs
index 18b6572..f9f50fa 100644
--- a/nitrokey/src/auth.rs
+++ b/nitrokey/src/auth.rs
@@ -1,7 +1,7 @@
 // Copyright (C) 2018-2019 Robin Krahl <robin.krahl@ireas.org>
 // SPDX-License-Identifier: MIT
 
-use std::ops::Deref;
+use std::ops;
 use std::os::raw::c_char;
 use std::os::raw::c_int;
 
@@ -49,7 +49,7 @@ pub trait Authenticate {
     ///         user.device()
     ///     },
     ///     Err((device, err)) => {
-    ///         println!("Could not authenticate as user: {}", err);
+    ///         eprintln!("Could not authenticate as user: {}", err);
     ///         device
     ///     },
     /// };
@@ -95,7 +95,7 @@ pub trait Authenticate {
     ///         admin.device()
     ///     },
     ///     Err((device, err)) => {
-    ///         println!("Could not authenticate as admin: {}", err);
+    ///         eprintln!("Could not authenticate as admin: {}", err);
     ///         device
     ///     },
     /// };
@@ -211,7 +211,7 @@ impl<T: Device> User<T> {
     }
 }
 
-impl<T: Device> Deref for User<T> {
+impl<T: Device> ops::Deref for User<T> {
     type Target = T;
 
     fn deref(&self) -> &Self::Target {
@@ -219,8 +219,14 @@ impl<T: Device> Deref for User<T> {
     }
 }
 
+impl<T: Device> ops::DerefMut for User<T> {
+    fn deref_mut(&mut self) -> &mut T {
+        &mut self.device
+    }
+}
+
 impl<T: Device> GenerateOtp for User<T> {
-    fn get_hotp_code(&self, slot: u8) -> Result<String, Error> {
+    fn get_hotp_code(&mut self, slot: u8) -> Result<String, Error> {
         result_from_string(unsafe {
             nitrokey_sys::NK_get_hotp_code_PIN(slot, self.temp_password_ptr())
         })
@@ -246,7 +252,7 @@ impl<T: Device> AuthenticatedDevice<T> for User<T> {
     }
 }
 
-impl<T: Device> Deref for Admin<T> {
+impl<T: Device> ops::Deref for Admin<T> {
     type Target = T;
 
     fn deref(&self) -> &Self::Target {
@@ -254,6 +260,12 @@ impl<T: Device> Deref for Admin<T> {
     }
 }
 
+impl<T: Device> ops::DerefMut for Admin<T> {
+    fn deref_mut(&mut self) -> &mut T {
+        &mut self.device
+    }
+}
+
 impl<T: Device> Admin<T> {
     /// Forgets the user authentication and returns an unauthenticated device.  This method
     /// consumes the authenticated device.  It does not perform any actual commands on the
@@ -278,18 +290,18 @@ impl<T: Device> Admin<T> {
     /// let device = nitrokey::connect()?;
     /// let config = Config::new(None, None, None, false);
     /// match device.authenticate_admin("12345678") {
-    ///     Ok(admin) => {
+    ///     Ok(mut admin) => {
     ///         admin.write_config(config);
     ///         ()
     ///     },
-    ///     Err((_, err)) => println!("Could not authenticate as admin: {}", err),
+    ///     Err((_, err)) => eprintln!("Could not authenticate as admin: {}", err),
     /// };
     /// #     Ok(())
     /// # }
     /// ```
     ///
     /// [`InvalidSlot`]: enum.LibraryError.html#variant.InvalidSlot
-    pub fn write_config(&self, config: Config) -> Result<(), Error> {
+    pub fn write_config(&mut self, config: Config) -> Result<(), Error> {
         let raw_config = RawConfig::try_from(config)?;
         get_command_result(unsafe {
             nitrokey_sys::NK_write_config(
@@ -305,7 +317,7 @@ impl<T: Device> Admin<T> {
 }
 
 impl<T: Device> ConfigureOtp for Admin<T> {
-    fn write_hotp_slot(&self, data: OtpSlotData, counter: u64) -> Result<(), Error> {
+    fn write_hotp_slot(&mut self, data: OtpSlotData, counter: u64) -> Result<(), Error> {
         let raw_data = RawOtpSlotData::new(data)?;
         get_command_result(unsafe {
             nitrokey_sys::NK_write_hotp_slot(
@@ -322,7 +334,7 @@ impl<T: Device> ConfigureOtp for Admin<T> {
         })
     }
 
-    fn write_totp_slot(&self, data: OtpSlotData, time_window: u16) -> Result<(), Error> {
+    fn write_totp_slot(&mut self, data: OtpSlotData, time_window: u16) -> Result<(), Error> {
         let raw_data = RawOtpSlotData::new(data)?;
         get_command_result(unsafe {
             nitrokey_sys::NK_write_totp_slot(
@@ -339,13 +351,13 @@ impl<T: Device> ConfigureOtp for Admin<T> {
         })
     }
 
-    fn erase_hotp_slot(&self, slot: u8) -> Result<(), Error> {
+    fn erase_hotp_slot(&mut self, slot: u8) -> Result<(), Error> {
         get_command_result(unsafe {
             nitrokey_sys::NK_erase_hotp_slot(slot, self.temp_password_ptr())
         })
     }
 
-    fn erase_totp_slot(&self, slot: u8) -> Result<(), Error> {
+    fn erase_totp_slot(&mut self, slot: u8) -> Result<(), Error> {
         get_command_result(unsafe {
             nitrokey_sys::NK_erase_totp_slot(slot, self.temp_password_ptr())
         })
diff --git a/nitrokey/src/device.rs b/nitrokey/src/device.rs
index 386ce94..f6492cd 100644
--- a/nitrokey/src/device.rs
+++ b/nitrokey/src/device.rs
@@ -12,7 +12,9 @@ use crate::config::{Config, RawConfig};
 use crate::error::{CommunicationError, Error};
 use crate::otp::GenerateOtp;
 use crate::pws::GetPasswordSafe;
-use crate::util::{get_command_result, get_cstring, get_last_error, result_from_string};
+use crate::util::{
+    get_command_result, get_cstring, get_last_error, result_from_string, result_or_error,
+};
 
 /// Available Nitrokey models.
 #[derive(Clone, Copy, Debug, PartialEq)]
@@ -76,7 +78,7 @@ impl fmt::Display for VolumeMode {
 ///         user.device()
 ///     },
 ///     Err((device, err)) => {
-///         println!("Could not authenticate as user: {}", err);
+///         eprintln!("Could not authenticate as user: {}", err);
 ///         device
 ///     },
 /// };
@@ -140,7 +142,7 @@ pub enum DeviceWrapper {
 ///         user.device()
 ///     },
 ///     Err((device, err)) => {
-///         println!("Could not authenticate as user: {}", err);
+///         eprintln!("Could not authenticate as user: {}", err);
 ///         device
 ///     },
 /// };
@@ -186,7 +188,7 @@ pub struct Pro {
 ///         user.device()
 ///     },
 ///     Err((device, err)) => {
-///         println!("Could not authenticate as user: {}", err);
+///         eprintln!("Could not authenticate as user: {}", err);
 ///         device
 ///     },
 /// };
@@ -323,7 +325,7 @@ pub trait Device: Authenticate + GetPasswordSafe + GenerateOtp + fmt::Debug {
     /// let device = nitrokey::connect()?;
     /// match device.get_serial_number() {
     ///     Ok(number) => println!("serial no: {}", number),
-    ///     Err(err) => println!("Could not get serial number: {}", err),
+    ///     Err(err) => eprintln!("Could not get serial number: {}", err),
     /// };
     /// #     Ok(())
     /// # }
@@ -343,13 +345,15 @@ pub trait Device: Authenticate + GetPasswordSafe + GenerateOtp + fmt::Debug {
     ///
     /// # fn try_main() -> Result<(), Error> {
     /// let device = nitrokey::connect()?;
-    /// let count = device.get_user_retry_count();
-    /// println!("{} remaining authentication attempts (user)", count);
+    /// match device.get_user_retry_count() {
+    ///     Ok(count) => println!("{} remaining authentication attempts (user)", count),
+    ///     Err(err) => eprintln!("Could not get user retry count: {}", err),
+    /// }
     /// #     Ok(())
     /// # }
     /// ```
-    fn get_user_retry_count(&self) -> u8 {
-        unsafe { nitrokey_sys::NK_get_user_retry_count() }
+    fn get_user_retry_count(&self) -> Result<u8, Error> {
+        result_or_error(unsafe { nitrokey_sys::NK_get_user_retry_count() })
     }
 
     /// Returns the number of remaining authentication attempts for the admin.  The total number of
@@ -364,15 +368,18 @@ pub trait Device: Authenticate + GetPasswordSafe + GenerateOtp + fmt::Debug {
     /// # fn try_main() -> Result<(), Error> {
     /// let device = nitrokey::connect()?;
     /// let count = device.get_admin_retry_count();
-    /// println!("{} remaining authentication attempts (admin)", count);
+    /// match device.get_admin_retry_count() {
+    ///     Ok(count) => println!("{} remaining authentication attempts (admin)", count),
+    ///     Err(err) => eprintln!("Could not get admin retry count: {}", err),
+    /// }
     /// #     Ok(())
     /// # }
     /// ```
-    fn get_admin_retry_count(&self) -> u8 {
-        unsafe { nitrokey_sys::NK_get_admin_retry_count() }
+    fn get_admin_retry_count(&self) -> Result<u8, Error> {
+        result_or_error(unsafe { nitrokey_sys::NK_get_admin_retry_count() })
     }
 
-    /// Returns the major part of the firmware version (should be zero).
+    /// Returns the firmware version.
     ///
     /// # Example
     ///
@@ -382,37 +389,24 @@ pub trait Device: Authenticate + GetPasswordSafe + GenerateOtp + fmt::Debug {
     ///
     /// # fn try_main() -> Result<(), Error> {
     /// let device = nitrokey::connect()?;
-    /// println!(
-    ///     "Firmware version: {}.{}",
-    ///     device.get_major_firmware_version(),
-    ///     device.get_minor_firmware_version(),
-    /// );
+    /// match device.get_firmware_version() {
+    ///     Ok(version) => println!("Firmware version: {}", version),
+    ///     Err(err) => eprintln!("Could not access firmware version: {}", err),
+    /// };
     /// #     Ok(())
     /// # }
     /// ```
-    fn get_major_firmware_version(&self) -> i32 {
-        unsafe { nitrokey_sys::NK_get_major_firmware_version() }
-    }
-
-    /// Returns the minor part of the firmware version (for example 8 for version 0.8).
-    ///
-    /// # Example
-    ///
-    /// ```no_run
-    /// use nitrokey::Device;
-    /// # use nitrokey::Error;
-    ///
-    /// # fn try_main() -> Result<(), Error> {
-    /// let device = nitrokey::connect()?;
-    /// println!(
-    ///     "Firmware version: {}.{}",
-    ///     device.get_major_firmware_version(),
-    ///     device.get_minor_firmware_version(),
-    /// );
-    /// #     Ok(())
-    /// # }
-    fn get_minor_firmware_version(&self) -> i32 {
-        unsafe { nitrokey_sys::NK_get_minor_firmware_version() }
+    fn get_firmware_version(&self) -> Result<FirmwareVersion, Error> {
+        let major = result_or_error(unsafe { nitrokey_sys::NK_get_major_firmware_version() })?;
+        let minor = result_or_error(unsafe { nitrokey_sys::NK_get_minor_firmware_version() })?;
+        let max = i32::from(u8::max_value());
+        if major < 0 || minor < 0 || major > max || minor > max {
+            return Err(Error::UnexpectedError);
+        }
+        Ok(FirmwareVersion {
+            major: major as u8,
+            minor: minor as u8,
+        })
     }
 
     /// Returns the current configuration of the Nitrokey device.
@@ -458,10 +452,10 @@ pub trait Device: Authenticate + GetPasswordSafe + GenerateOtp + fmt::Debug {
     /// # use nitrokey::Error;
     ///
     /// # fn try_main() -> Result<(), Error> {
-    /// let device = nitrokey::connect()?;
+    /// let mut device = nitrokey::connect()?;
     /// match device.change_admin_pin("12345678", "12345679") {
     ///     Ok(()) => println!("Updated admin PIN."),
-    ///     Err(err) => println!("Failed to update admin PIN: {}", err),
+    ///     Err(err) => eprintln!("Failed to update admin PIN: {}", err),
     /// };
     /// #     Ok(())
     /// # }
@@ -469,7 +463,7 @@ pub trait Device: Authenticate + GetPasswordSafe + GenerateOtp + fmt::Debug {
     ///
     /// [`InvalidString`]: enum.LibraryError.html#variant.InvalidString
     /// [`WrongPassword`]: enum.CommandError.html#variant.WrongPassword
-    fn change_admin_pin(&self, current: &str, new: &str) -> Result<(), Error> {
+    fn change_admin_pin(&mut self, current: &str, new: &str) -> Result<(), Error> {
         let current_string = get_cstring(current)?;
         let new_string = get_cstring(new)?;
         get_command_result(unsafe {
@@ -491,10 +485,10 @@ pub trait Device: Authenticate + GetPasswordSafe + GenerateOtp + fmt::Debug {
     /// # use nitrokey::Error;
     ///
     /// # fn try_main() -> Result<(), Error> {
-    /// let device = nitrokey::connect()?;
+    /// let mut device = nitrokey::connect()?;
     /// match device.change_user_pin("123456", "123457") {
     ///     Ok(()) => println!("Updated admin PIN."),
-    ///     Err(err) => println!("Failed to update admin PIN: {}", err),
+    ///     Err(err) => eprintln!("Failed to update admin PIN: {}", err),
     /// };
     /// #     Ok(())
     /// # }
@@ -502,7 +496,7 @@ pub trait Device: Authenticate + GetPasswordSafe + GenerateOtp + fmt::Debug {
     ///
     /// [`InvalidString`]: enum.LibraryError.html#variant.InvalidString
     /// [`WrongPassword`]: enum.CommandError.html#variant.WrongPassword
-    fn change_user_pin(&self, current: &str, new: &str) -> Result<(), Error> {
+    fn change_user_pin(&mut self, current: &str, new: &str) -> Result<(), Error> {
         let current_string = get_cstring(current)?;
         let new_string = get_cstring(new)?;
         get_command_result(unsafe {
@@ -524,10 +518,10 @@ pub trait Device: Authenticate + GetPasswordSafe + GenerateOtp + fmt::Debug {
     /// # use nitrokey::Error;
     ///
     /// # fn try_main() -> Result<(), Error> {
-    /// let device = nitrokey::connect()?;
+    /// let mut device = nitrokey::connect()?;
     /// match device.unlock_user_pin("12345678", "123456") {
     ///     Ok(()) => println!("Unlocked user PIN."),
-    ///     Err(err) => println!("Failed to unlock user PIN: {}", err),
+    ///     Err(err) => eprintln!("Failed to unlock user PIN: {}", err),
     /// };
     /// #     Ok(())
     /// # }
@@ -535,7 +529,7 @@ pub trait Device: Authenticate + GetPasswordSafe + GenerateOtp + fmt::Debug {
     ///
     /// [`InvalidString`]: enum.LibraryError.html#variant.InvalidString
     /// [`WrongPassword`]: enum.CommandError.html#variant.WrongPassword
-    fn unlock_user_pin(&self, admin_pin: &str, user_pin: &str) -> Result<(), Error> {
+    fn unlock_user_pin(&mut self, admin_pin: &str, user_pin: &str) -> Result<(), Error> {
         let admin_pin_string = get_cstring(admin_pin)?;
         let user_pin_string = get_cstring(user_pin)?;
         get_command_result(unsafe {
@@ -558,15 +552,15 @@ pub trait Device: Authenticate + GetPasswordSafe + GenerateOtp + fmt::Debug {
     /// # use nitrokey::Error;
     ///
     /// # fn try_main() -> Result<(), Error> {
-    /// let device = nitrokey::connect()?;
+    /// let mut device = nitrokey::connect()?;
     /// match device.lock() {
     ///     Ok(()) => println!("Locked the Nitrokey device."),
-    ///     Err(err) => println!("Could not lock the Nitrokey device: {}", err),
+    ///     Err(err) => eprintln!("Could not lock the Nitrokey device: {}", err),
     /// };
     /// #     Ok(())
     /// # }
     /// ```
-    fn lock(&self) -> Result<(), Error> {
+    fn lock(&mut self) -> Result<(), Error> {
         get_command_result(unsafe { nitrokey_sys::NK_lock_device() })
     }
 
@@ -589,17 +583,17 @@ pub trait Device: Authenticate + GetPasswordSafe + GenerateOtp + fmt::Debug {
     /// # use nitrokey::Error;
     ///
     /// # fn try_main() -> Result<(), Error> {
-    /// let device = nitrokey::connect()?;
+    /// let mut device = nitrokey::connect()?;
     /// match device.factory_reset("12345678") {
     ///     Ok(()) => println!("Performed a factory reset."),
-    ///     Err(err) => println!("Could not perform a factory reset: {}", err),
+    ///     Err(err) => eprintln!("Could not perform a factory reset: {}", err),
     /// };
     /// #     Ok(())
     /// # }
     /// ```
     ///
     /// [`build_aes_key`]: #method.build_aes_key
-    fn factory_reset(&self, admin_pin: &str) -> Result<(), Error> {
+    fn factory_reset(&mut self, admin_pin: &str) -> Result<(), Error> {
         let admin_pin_string = get_cstring(admin_pin)?;
         get_command_result(unsafe { nitrokey_sys::NK_factory_reset(admin_pin_string.as_ptr()) })
     }
@@ -623,17 +617,17 @@ pub trait Device: Authenticate + GetPasswordSafe + GenerateOtp + fmt::Debug {
     /// # use nitrokey::Error;
     ///
     /// # fn try_main() -> Result<(), Error> {
-    /// let device = nitrokey::connect()?;
+    /// let mut device = nitrokey::connect()?;
     /// match device.build_aes_key("12345678") {
     ///     Ok(()) => println!("New AES keys have been built."),
-    ///     Err(err) => println!("Could not build new AES keys: {}", err),
+    ///     Err(err) => eprintln!("Could not build new AES keys: {}", err),
     /// };
     /// #     Ok(())
     /// # }
     /// ```
     ///
     /// [`factory_reset`]: #method.factory_reset
-    fn build_aes_key(&self, admin_pin: &str) -> Result<(), Error> {
+    fn build_aes_key(&mut self, admin_pin: &str) -> Result<(), Error> {
         let admin_pin_string = get_cstring(admin_pin)?;
         get_command_result(unsafe { nitrokey_sys::NK_build_aes_key(admin_pin_string.as_ptr()) })
     }
@@ -655,7 +649,7 @@ pub trait Device: Authenticate + GetPasswordSafe + GenerateOtp + fmt::Debug {
 ///
 /// match nitrokey::connect() {
 ///     Ok(device) => do_something(device),
-///     Err(err) => println!("Could not connect to a Nitrokey: {}", err),
+///     Err(err) => eprintln!("Could not connect to a Nitrokey: {}", err),
 /// }
 /// ```
 ///
@@ -687,7 +681,7 @@ pub fn connect() -> Result<DeviceWrapper, Error> {
 ///
 /// match nitrokey::connect_model(Model::Pro) {
 ///     Ok(device) => do_something(device),
-///     Err(err) => println!("Could not connect to a Nitrokey Pro: {}", err),
+///     Err(err) => eprintln!("Could not connect to a Nitrokey Pro: {}", err),
 /// }
 /// ```
 ///
@@ -734,6 +728,13 @@ impl DeviceWrapper {
             DeviceWrapper::Pro(ref pro) => pro,
         }
     }
+
+    fn device_mut(&mut self) -> &mut dyn Device {
+        match *self {
+            DeviceWrapper::Storage(ref mut storage) => storage,
+            DeviceWrapper::Pro(ref mut pro) => pro,
+        }
+    }
 }
 
 impl From<Pro> for DeviceWrapper {
@@ -757,8 +758,8 @@ impl GenerateOtp for DeviceWrapper {
         self.device().get_totp_slot_name(slot)
     }
 
-    fn get_hotp_code(&self, slot: u8) -> Result<String, Error> {
-        self.device().get_hotp_code(slot)
+    fn get_hotp_code(&mut self, slot: u8) -> Result<String, Error> {
+        self.device_mut().get_hotp_code(slot)
     }
 
     fn get_totp_code(&self, slot: u8) -> Result<String, Error> {
@@ -791,7 +792,7 @@ impl Pro {
     ///
     /// match nitrokey::Pro::connect() {
     ///     Ok(device) => use_pro(device),
-    ///     Err(err) => println!("Could not connect to the Nitrokey Pro: {}", err),
+    ///     Err(err) => eprintln!("Could not connect to the Nitrokey Pro: {}", err),
     /// }
     /// ```
     ///
@@ -844,7 +845,7 @@ impl Storage {
     ///
     /// match nitrokey::Storage::connect() {
     ///     Ok(device) => use_storage(device),
-    ///     Err(err) => println!("Could not connect to the Nitrokey Storage: {}", err),
+    ///     Err(err) => eprintln!("Could not connect to the Nitrokey Storage: {}", err),
     /// }
     /// ```
     ///
@@ -881,10 +882,10 @@ impl Storage {
     /// # use nitrokey::Error;
     ///
     /// # fn try_main() -> Result<(), Error> {
-    /// let device = nitrokey::Storage::connect()?;
+    /// let mut device = nitrokey::Storage::connect()?;
     /// match device.change_update_pin("12345678", "87654321") {
     ///     Ok(()) => println!("Updated update PIN."),
-    ///     Err(err) => println!("Failed to update update PIN: {}", err),
+    ///     Err(err) => eprintln!("Failed to update update PIN: {}", err),
     /// };
     /// #     Ok(())
     /// # }
@@ -892,7 +893,7 @@ impl Storage {
     ///
     /// [`InvalidString`]: enum.LibraryError.html#variant.InvalidString
     /// [`WrongPassword`]: enum.CommandError.html#variant.WrongPassword
-    pub fn change_update_pin(&self, current: &str, new: &str) -> Result<(), Error> {
+    pub fn change_update_pin(&mut self, current: &str, new: &str) -> Result<(), Error> {
         let current_string = get_cstring(current)?;
         let new_string = get_cstring(new)?;
         get_command_result(unsafe {
@@ -918,10 +919,10 @@ impl Storage {
     /// # use nitrokey::Error;
     ///
     /// # fn try_main() -> Result<(), Error> {
-    /// let device = nitrokey::Storage::connect()?;
+    /// let mut device = nitrokey::Storage::connect()?;
     /// match device.enable_firmware_update("12345678") {
     ///     Ok(()) => println!("Nitrokey entered update mode."),
-    ///     Err(err) => println!("Could not enter update mode: {}", err),
+    ///     Err(err) => eprintln!("Could not enter update mode: {}", err),
     /// };
     /// #     Ok(())
     /// # }
@@ -929,7 +930,7 @@ impl Storage {
     ///
     /// [`InvalidString`]: enum.LibraryError.html#variant.InvalidString
     /// [`WrongPassword`]: enum.CommandError.html#variant.WrongPassword
-    pub fn enable_firmware_update(&self, update_pin: &str) -> Result<(), Error> {
+    pub fn enable_firmware_update(&mut self, update_pin: &str) -> Result<(), Error> {
         let update_pin_string = get_cstring(update_pin)?;
         get_command_result(unsafe {
             nitrokey_sys::NK_enable_firmware_update(update_pin_string.as_ptr())
@@ -952,10 +953,10 @@ impl Storage {
     /// # use nitrokey::Error;
     ///
     /// # fn try_main() -> Result<(), Error> {
-    /// let device = nitrokey::Storage::connect()?;
+    /// let mut device = nitrokey::Storage::connect()?;
     /// match device.enable_encrypted_volume("123456") {
     ///     Ok(()) => println!("Enabled the encrypted volume."),
-    ///     Err(err) => println!("Could not enable the encrypted volume: {}", err),
+    ///     Err(err) => eprintln!("Could not enable the encrypted volume: {}", err),
     /// };
     /// #     Ok(())
     /// # }
@@ -963,7 +964,7 @@ impl Storage {
     ///
     /// [`InvalidString`]: enum.LibraryError.html#variant.InvalidString
     /// [`WrongPassword`]: enum.CommandError.html#variant.WrongPassword
-    pub fn enable_encrypted_volume(&self, user_pin: &str) -> Result<(), Error> {
+    pub fn enable_encrypted_volume(&mut self, user_pin: &str) -> Result<(), Error> {
         let user_pin = get_cstring(user_pin)?;
         get_command_result(unsafe { nitrokey_sys::NK_unlock_encrypted_volume(user_pin.as_ptr()) })
     }
@@ -981,7 +982,7 @@ impl Storage {
     /// fn use_volume() {}
     ///
     /// # fn try_main() -> Result<(), Error> {
-    /// let device = nitrokey::Storage::connect()?;
+    /// let mut device = nitrokey::Storage::connect()?;
     /// match device.enable_encrypted_volume("123456") {
     ///     Ok(()) => {
     ///         println!("Enabled the encrypted volume.");
@@ -989,16 +990,16 @@ impl Storage {
     ///         match device.disable_encrypted_volume() {
     ///             Ok(()) => println!("Disabled the encrypted volume."),
     ///             Err(err) => {
-    ///                 println!("Could not disable the encrypted volume: {}", err);
+    ///                 eprintln!("Could not disable the encrypted volume: {}", err);
     ///             },
     ///         };
     ///     },
-    ///     Err(err) => println!("Could not enable the encrypted volume: {}", err),
+    ///     Err(err) => eprintln!("Could not enable the encrypted volume: {}", err),
     /// };
     /// #     Ok(())
     /// # }
     /// ```
-    pub fn disable_encrypted_volume(&self) -> Result<(), Error> {
+    pub fn disable_encrypted_volume(&mut self) -> Result<(), Error> {
         get_command_result(unsafe { nitrokey_sys::NK_lock_encrypted_volume() })
     }
 
@@ -1027,11 +1028,11 @@ impl Storage {
     /// # use nitrokey::Error;
     ///
     /// # fn try_main() -> Result<(), Error> {
-    /// let device = nitrokey::Storage::connect()?;
+    /// let mut device = nitrokey::Storage::connect()?;
     /// device.enable_encrypted_volume("123445")?;
     /// match device.enable_hidden_volume("hidden-pw") {
     ///     Ok(()) => println!("Enabled a hidden volume."),
-    ///     Err(err) => println!("Could not enable the hidden volume: {}", err),
+    ///     Err(err) => eprintln!("Could not enable the hidden volume: {}", err),
     /// };
     /// #     Ok(())
     /// # }
@@ -1040,7 +1041,7 @@ impl Storage {
     /// [`enable_encrypted_volume`]: #method.enable_encrypted_volume
     /// [`AesDecryptionFailed`]: enum.CommandError.html#variant.AesDecryptionFailed
     /// [`InvalidString`]: enum.LibraryError.html#variant.InvalidString
-    pub fn enable_hidden_volume(&self, volume_password: &str) -> Result<(), Error> {
+    pub fn enable_hidden_volume(&mut self, volume_password: &str) -> Result<(), Error> {
         let volume_password = get_cstring(volume_password)?;
         get_command_result(unsafe {
             nitrokey_sys::NK_unlock_hidden_volume(volume_password.as_ptr())
@@ -1060,7 +1061,7 @@ impl Storage {
     /// fn use_volume() {}
     ///
     /// # fn try_main() -> Result<(), Error> {
-    /// let device = nitrokey::Storage::connect()?;
+    /// let mut device = nitrokey::Storage::connect()?;
     /// device.enable_encrypted_volume("123445")?;
     /// match device.enable_hidden_volume("hidden-pw") {
     ///     Ok(()) => {
@@ -1069,16 +1070,16 @@ impl Storage {
     ///         match device.disable_hidden_volume() {
     ///             Ok(()) => println!("Disabled the hidden volume."),
     ///             Err(err) => {
-    ///                 println!("Could not disable the hidden volume: {}", err);
+    ///                 eprintln!("Could not disable the hidden volume: {}", err);
     ///             },
     ///         };
     ///     },
-    ///     Err(err) => println!("Could not enable the hidden volume: {}", err),
+    ///     Err(err) => eprintln!("Could not enable the hidden volume: {}", err),
     /// };
     /// #     Ok(())
     /// # }
     /// ```
-    pub fn disable_hidden_volume(&self) -> Result<(), Error> {
+    pub fn disable_hidden_volume(&mut self) -> Result<(), Error> {
         get_command_result(unsafe { nitrokey_sys::NK_lock_hidden_volume() })
     }
 
@@ -1107,7 +1108,7 @@ impl Storage {
     /// # use nitrokey::Error;
     ///
     /// # fn try_main() -> Result<(), Error> {
-    /// let device = nitrokey::Storage::connect()?;
+    /// let mut device = nitrokey::Storage::connect()?;
     /// device.enable_encrypted_volume("123445")?;
     /// device.create_hidden_volume(0, 0, 100, "hidden-pw")?;
     /// #     Ok(())
@@ -1117,7 +1118,7 @@ impl Storage {
     /// [`AesDecryptionFailed`]: enum.CommandError.html#variant.AesDecryptionFailed
     /// [`InvalidString`]: enum.LibraryError.html#variant.InvalidString
     pub fn create_hidden_volume(
-        &self,
+        &mut self,
         slot: u8,
         start: u8,
         end: u8,
@@ -1147,10 +1148,10 @@ impl Storage {
     /// use nitrokey::VolumeMode;
     ///
     /// # fn try_main() -> Result<(), Error> {
-    /// let device = nitrokey::Storage::connect()?;
-    /// match device.set_unencrypted_volume_mode("123456", VolumeMode::ReadWrite) {
+    /// let mut device = nitrokey::Storage::connect()?;
+    /// match device.set_unencrypted_volume_mode("12345678", VolumeMode::ReadWrite) {
     ///     Ok(()) => println!("Set the unencrypted volume to read-write mode."),
-    ///     Err(err) => println!("Could not set the unencrypted volume to read-write mode: {}", err),
+    ///     Err(err) => eprintln!("Could not set the unencrypted volume to read-write mode: {}", err),
     /// };
     /// #     Ok(())
     /// # }
@@ -1159,7 +1160,7 @@ impl Storage {
     /// [`InvalidString`]: enum.LibraryError.html#variant.InvalidString
     /// [`WrongPassword`]: enum.CommandError.html#variant.WrongPassword
     pub fn set_unencrypted_volume_mode(
-        &self,
+        &mut self,
         admin_pin: &str,
         mode: VolumeMode,
     ) -> Result<(), Error> {
@@ -1175,6 +1176,51 @@ impl Storage {
         get_command_result(result)
     }
 
+    /// Sets the access mode of the encrypted volume.
+    ///
+    /// This command will reconnect the encrypted volume so buffers should be flushed before
+    /// calling it.  It is only available in firmware version 0.49.
+    ///
+    /// # Errors
+    ///
+    /// - [`InvalidString`][] if the provided password contains a null byte
+    /// - [`WrongPassword`][] if the provided admin password is wrong
+    ///
+    /// # Example
+    ///
+    /// ```no_run
+    /// # use nitrokey::Error;
+    /// use nitrokey::VolumeMode;
+    ///
+    /// # fn try_main() -> Result<(), Error> {
+    /// let mut device = nitrokey::Storage::connect()?;
+    /// match device.set_encrypted_volume_mode("12345678", VolumeMode::ReadWrite) {
+    ///     Ok(()) => println!("Set the encrypted volume to read-write mode."),
+    ///     Err(err) => eprintln!("Could not set the encrypted volume to read-write mode: {}", err),
+    /// };
+    /// #     Ok(())
+    /// # }
+    /// ```
+    ///
+    /// [`InvalidString`]: enum.LibraryError.html#variant.InvalidString
+    /// [`WrongPassword`]: enum.CommandError.html#variant.WrongPassword
+    pub fn set_encrypted_volume_mode(
+        &mut self,
+        admin_pin: &str,
+        mode: VolumeMode,
+    ) -> Result<(), Error> {
+        let admin_pin = get_cstring(admin_pin)?;
+        let result = match mode {
+            VolumeMode::ReadOnly => unsafe {
+                nitrokey_sys::NK_set_encrypted_read_only(admin_pin.as_ptr())
+            },
+            VolumeMode::ReadWrite => unsafe {
+                nitrokey_sys::NK_set_encrypted_read_write(admin_pin.as_ptr())
+            },
+        };
+        get_command_result(result)
+    }
+
     /// Returns the status of the connected storage device.
     ///
     /// # Example
@@ -1190,7 +1236,7 @@ impl Storage {
     ///     Ok(status) => {
     ///         println!("SD card ID: {:#x}", status.serial_number_sd_card);
     ///     },
-    ///     Err(err) => println!("Could not get Storage status: {}", err),
+    ///     Err(err) => eprintln!("Could not get Storage status: {}", err),
     /// };
     /// #     Ok(())
     /// # }
@@ -1234,7 +1280,7 @@ impl Storage {
     ///         println!("SD card ID:   {:#x}", data.sd_card.serial_number);
     ///         println!("SD card size: {} GB", data.sd_card.size);
     ///     },
-    ///     Err(err) => println!("Could not get Storage production info: {}", err),
+    ///     Err(err) => eprintln!("Could not get Storage production info: {}", err),
     /// };
     /// #     Ok(())
     /// # }
@@ -1276,10 +1322,10 @@ impl Storage {
     /// # use nitrokey::Error;
     ///
     /// # fn try_main() -> Result<(), Error> {
-    /// let device = nitrokey::Storage::connect()?;
+    /// let mut device = nitrokey::Storage::connect()?;
     /// match device.clear_new_sd_card_warning("12345678") {
     ///     Ok(()) => println!("Cleared the new SD card warning."),
-    ///     Err(err) => println!("Could not set the clear the new SD card warning: {}", err),
+    ///     Err(err) => eprintln!("Could not set the clear the new SD card warning: {}", err),
     /// };
     /// #     Ok(())
     /// # }
@@ -1287,7 +1333,7 @@ impl Storage {
     ///
     /// [`InvalidString`]: enum.LibraryError.html#variant.InvalidString
     /// [`WrongPassword`]: enum.CommandError.html#variant.WrongPassword
-    pub fn clear_new_sd_card_warning(&self, admin_pin: &str) -> Result<(), Error> {
+    pub fn clear_new_sd_card_warning(&mut self, admin_pin: &str) -> Result<(), Error> {
         let admin_pin = get_cstring(admin_pin)?;
         get_command_result(unsafe {
             nitrokey_sys::NK_clear_new_sd_card_warning(admin_pin.as_ptr())
@@ -1295,7 +1341,7 @@ impl Storage {
     }
 
     /// Blinks the red and green LED alternatively and infinitely until the device is reconnected.
-    pub fn wink(&self) -> Result<(), Error> {
+    pub fn wink(&mut self) -> Result<(), Error> {
         get_command_result(unsafe { nitrokey_sys::NK_wink() })
     }
 
@@ -1315,7 +1361,7 @@ impl Storage {
     ///
     /// [`InvalidString`]: enum.LibraryError.html#variant.InvalidString
     /// [`WrongPassword`]: enum.CommandError.html#variant.WrongPassword
-    pub fn export_firmware(&self, admin_pin: &str) -> Result<(), Error> {
+    pub fn export_firmware(&mut self, admin_pin: &str) -> Result<(), Error> {
         let admin_pin_string = get_cstring(admin_pin)?;
         get_command_result(unsafe { nitrokey_sys::NK_export_firmware(admin_pin_string.as_ptr()) })
     }
diff --git a/nitrokey/src/lib.rs b/nitrokey/src/lib.rs
index f2d524e..c35829c 100644
--- a/nitrokey/src/lib.rs
+++ b/nitrokey/src/lib.rs
@@ -47,13 +47,13 @@
 //! let device = nitrokey::connect()?;
 //! let slot_data = OtpSlotData::new(1, "test", "01234567890123456689", OtpMode::SixDigits);
 //! match device.authenticate_admin("12345678") {
-//!     Ok(admin) => {
+//!     Ok(mut admin) => {
 //!         match admin.write_hotp_slot(slot_data, 0) {
 //!             Ok(()) => println!("Successfully wrote slot."),
-//!             Err(err) => println!("Could not write slot: {}", err),
+//!             Err(err) => eprintln!("Could not write slot: {}", err),
 //!         }
 //!     },
-//!     Err((_, err)) => println!("Could not authenticate as admin: {}", err),
+//!     Err((_, err)) => eprintln!("Could not authenticate as admin: {}", err),
 //! }
 //! #     Ok(())
 //! # }
@@ -66,10 +66,10 @@
 //! # use nitrokey::Error;
 //!
 //! # fn try_main() -> Result<(), Error> {
-//! let device = nitrokey::connect()?;
+//! let mut device = nitrokey::connect()?;
 //! match device.get_hotp_code(1) {
 //!     Ok(code) => println!("Generated HOTP code: {}", code),
-//!     Err(err) => println!("Could not generate HOTP code: {}", err),
+//!     Err(err) => eprintln!("Could not generate HOTP code: {}", err),
 //! }
 //! #     Ok(())
 //! # }
diff --git a/nitrokey/src/otp.rs b/nitrokey/src/otp.rs
index 6e0379b..ee142c7 100644
--- a/nitrokey/src/otp.rs
+++ b/nitrokey/src/otp.rs
@@ -38,13 +38,13 @@ pub trait ConfigureOtp {
     /// let device = nitrokey::connect()?;
     /// let slot_data = OtpSlotData::new(1, "test", "01234567890123456689", OtpMode::SixDigits);
     /// match device.authenticate_admin("12345678") {
-    ///     Ok(admin) => {
+    ///     Ok(mut admin) => {
     ///         match admin.write_hotp_slot(slot_data, 0) {
     ///             Ok(()) => println!("Successfully wrote slot."),
-    ///             Err(err) => println!("Could not write slot: {}", err),
+    ///             Err(err) => eprintln!("Could not write slot: {}", err),
     ///         }
     ///     },
-    ///     Err((_, err)) => println!("Could not authenticate as admin: {}", err),
+    ///     Err((_, err)) => eprintln!("Could not authenticate as admin: {}", err),
     /// }
     /// #     Ok(())
     /// # }
@@ -53,7 +53,7 @@ pub trait ConfigureOtp {
     /// [`InvalidSlot`]: enum.LibraryError.html#variant.InvalidSlot
     /// [`InvalidString`]: enum.LibraryError.html#variant.InvalidString
     /// [`NoName`]: enum.CommandError.html#variant.NoName
-    fn write_hotp_slot(&self, data: OtpSlotData, counter: u64) -> Result<(), Error>;
+    fn write_hotp_slot(&mut self, data: OtpSlotData, counter: u64) -> Result<(), Error>;
 
     /// Configure a TOTP slot with the given data and set the TOTP time window to the given value
     /// (default 30).
@@ -74,13 +74,13 @@ pub trait ConfigureOtp {
     /// let device = nitrokey::connect()?;
     /// let slot_data = OtpSlotData::new(1, "test", "01234567890123456689", OtpMode::EightDigits);
     /// match device.authenticate_admin("12345678") {
-    ///     Ok(admin) => {
+    ///     Ok(mut admin) => {
     ///         match admin.write_totp_slot(slot_data, 30) {
     ///             Ok(()) => println!("Successfully wrote slot."),
-    ///             Err(err) => println!("Could not write slot: {}", err),
+    ///             Err(err) => eprintln!("Could not write slot: {}", err),
     ///         }
     ///     },
-    ///     Err((_, err)) => println!("Could not authenticate as admin: {}", err),
+    ///     Err((_, err)) => eprintln!("Could not authenticate as admin: {}", err),
     /// }
     /// #     Ok(())
     /// # }
@@ -89,7 +89,7 @@ pub trait ConfigureOtp {
     /// [`InvalidSlot`]: enum.LibraryError.html#variant.InvalidSlot
     /// [`InvalidString`]: enum.LibraryError.html#variant.InvalidString
     /// [`NoName`]: enum.CommandError.html#variant.NoName
-    fn write_totp_slot(&self, data: OtpSlotData, time_window: u16) -> Result<(), Error>;
+    fn write_totp_slot(&mut self, data: OtpSlotData, time_window: u16) -> Result<(), Error>;
 
     /// Erases an HOTP slot.
     ///
@@ -106,20 +106,20 @@ pub trait ConfigureOtp {
     /// # fn try_main() -> Result<(), Error> {
     /// let device = nitrokey::connect()?;
     /// match device.authenticate_admin("12345678") {
-    ///     Ok(admin) => {
+    ///     Ok(mut admin) => {
     ///         match admin.erase_hotp_slot(1) {
     ///             Ok(()) => println!("Successfully erased slot."),
-    ///             Err(err) => println!("Could not erase slot: {}", err),
+    ///             Err(err) => eprintln!("Could not erase slot: {}", err),
     ///         }
     ///     },
-    ///     Err((_, err)) => println!("Could not authenticate as admin: {}", err),
+    ///     Err((_, err)) => eprintln!("Could not authenticate as admin: {}", err),
     /// }
     /// #     Ok(())
     /// # }
     /// ```
     ///
     /// [`InvalidSlot`]: enum.LibraryError.html#variant.InvalidSlot
-    fn erase_hotp_slot(&self, slot: u8) -> Result<(), Error>;
+    fn erase_hotp_slot(&mut self, slot: u8) -> Result<(), Error>;
 
     /// Erases a TOTP slot.
     ///
@@ -136,20 +136,20 @@ pub trait ConfigureOtp {
     /// # fn try_main() -> Result<(), Error> {
     /// let device = nitrokey::connect()?;
     /// match device.authenticate_admin("12345678") {
-    ///     Ok(admin) => {
+    ///     Ok(mut admin) => {
     ///         match admin.erase_totp_slot(1) {
     ///             Ok(()) => println!("Successfully erased slot."),
-    ///             Err(err) => println!("Could not erase slot: {}", err),
+    ///             Err(err) => eprintln!("Could not erase slot: {}", err),
     ///         }
     ///     },
-    ///     Err((_, err)) => println!("Could not authenticate as admin: {}", err),
+    ///     Err((_, err)) => eprintln!("Could not authenticate as admin: {}", err),
     /// }
     /// #     Ok(())
     /// # }
     /// ```
     ///
     /// [`InvalidSlot`]: enum.LibraryError.html#variant.InvalidSlot
-    fn erase_totp_slot(&self, slot: u8) -> Result<(), Error>;
+    fn erase_totp_slot(&mut self, slot: u8) -> Result<(), Error>;
 }
 
 /// Provides methods to generate OTP codes and to query OTP slots on a Nitrokey
@@ -171,11 +171,11 @@ pub trait GenerateOtp {
     /// # use nitrokey::Error;
     ///
     /// # fn try_main() -> Result<(), Error> {
-    /// let device = nitrokey::connect()?;
+    /// let mut device = nitrokey::connect()?;
     /// let time = time::SystemTime::now().duration_since(time::UNIX_EPOCH);
     /// match time {
     ///     Ok(time) => device.set_time(time.as_secs(), false)?,
-    ///     Err(_) => println!("The system time is before the Unix epoch!"),
+    ///     Err(_) => eprintln!("The system time is before the Unix epoch!"),
     /// }
     /// #     Ok(())
     /// # }
@@ -187,7 +187,7 @@ pub trait GenerateOtp {
     ///
     /// [`get_totp_code`]: #method.get_totp_code
     /// [`Timestamp`]: enum.CommandError.html#variant.Timestamp
-    fn set_time(&self, time: u64, force: bool) -> Result<(), Error> {
+    fn set_time(&mut self, time: u64, force: bool) -> Result<(), Error> {
         let result = if force {
             unsafe { nitrokey_sys::NK_totp_set_time(time) }
         } else {
@@ -212,8 +212,8 @@ pub trait GenerateOtp {
     /// let device = nitrokey::connect()?;
     /// match device.get_hotp_slot_name(1) {
     ///     Ok(name) => println!("HOTP slot 1: {}", name),
-    ///     Err(Error::CommandError(CommandError::SlotNotProgrammed)) => println!("HOTP slot 1 not programmed"),
-    ///     Err(err) => println!("Could not get slot name: {}", err),
+    ///     Err(Error::CommandError(CommandError::SlotNotProgrammed)) => eprintln!("HOTP slot 1 not programmed"),
+    ///     Err(err) => eprintln!("Could not get slot name: {}", err),
     /// };
     /// #     Ok(())
     /// # }
@@ -241,8 +241,8 @@ pub trait GenerateOtp {
     /// let device = nitrokey::connect()?;
     /// match device.get_totp_slot_name(1) {
     ///     Ok(name) => println!("TOTP slot 1: {}", name),
-    ///     Err(Error::CommandError(CommandError::SlotNotProgrammed)) => println!("TOTP slot 1 not programmed"),
-    ///     Err(err) => println!("Could not get slot name: {}", err),
+    ///     Err(Error::CommandError(CommandError::SlotNotProgrammed)) => eprintln!("TOTP slot 1 not programmed"),
+    ///     Err(err) => eprintln!("Could not get slot name: {}", err),
     /// };
     /// #     Ok(())
     /// # }
@@ -270,7 +270,7 @@ pub trait GenerateOtp {
     /// # use nitrokey::Error;
     ///
     /// # fn try_main() -> Result<(), Error> {
-    /// let device = nitrokey::connect()?;
+    /// let mut device = nitrokey::connect()?;
     /// let code = device.get_hotp_code(1)?;
     /// println!("Generated HOTP code on slot 1: {}", code);
     /// #     Ok(())
@@ -281,7 +281,7 @@ pub trait GenerateOtp {
     /// [`InvalidSlot`]: enum.LibraryError.html#variant.InvalidSlot
     /// [`NotAuthorized`]: enum.CommandError.html#variant.NotAuthorized
     /// [`SlotNotProgrammed`]: enum.CommandError.html#variant.SlotNotProgrammed
-    fn get_hotp_code(&self, slot: u8) -> Result<String, Error> {
+    fn get_hotp_code(&mut self, slot: u8) -> Result<String, Error> {
         result_from_string(unsafe { nitrokey_sys::NK_get_hotp_code(slot) })
     }
 
@@ -305,7 +305,7 @@ pub trait GenerateOtp {
     /// # use nitrokey::Error;
     ///
     /// # fn try_main() -> Result<(), Error> {
-    /// let device = nitrokey::connect()?;
+    /// let mut device = nitrokey::connect()?;
     /// let time = time::SystemTime::now().duration_since(time::UNIX_EPOCH);
     /// match time {
     ///     Ok(time) => {
@@ -313,7 +313,7 @@ pub trait GenerateOtp {
     ///         let code = device.get_totp_code(1)?;
     ///         println!("Generated TOTP code on slot 1: {}", code);
     ///     },
-    ///     Err(_) => println!("Timestamps before 1970-01-01 are not supported!"),
+    ///     Err(_) => eprintln!("Timestamps before 1970-01-01 are not supported!"),
     /// }
     /// #     Ok(())
     /// # }
diff --git a/nitrokey/src/pws.rs b/nitrokey/src/pws.rs
index fcf057b..371de6e 100644
--- a/nitrokey/src/pws.rs
+++ b/nitrokey/src/pws.rs
@@ -43,9 +43,10 @@ pub const SLOT_COUNT: u8 = 16;
 /// }
 ///
 /// # fn try_main() -> Result<(), Error> {
-/// let device = nitrokey::connect()?;
+/// let mut device = nitrokey::connect()?;
 /// let pws = device.get_password_safe("123456")?;
 /// use_password_safe(&pws);
+/// drop(pws);
 /// device.lock()?;
 /// #     Ok(())
 /// # }
@@ -97,14 +98,14 @@ pub trait GetPasswordSafe {
     /// fn use_password_safe(pws: &PasswordSafe) {}
     ///
     /// # fn try_main() -> Result<(), Error> {
-    /// let device = nitrokey::connect()?;
+    /// let mut device = nitrokey::connect()?;
     /// match device.get_password_safe("123456") {
     ///     Ok(pws) => {
     ///         use_password_safe(&pws);
-    ///         device.lock()?;
     ///     },
-    ///     Err(err) => println!("Could not open the password safe: {}", err),
+    ///     Err(err) => eprintln!("Could not open the password safe: {}", err),
     /// };
+    /// device.lock()?;
     /// #     Ok(())
     /// # }
     /// ```
@@ -116,7 +117,7 @@ pub trait GetPasswordSafe {
     /// [`InvalidString`]: enum.LibraryError.html#variant.InvalidString
     /// [`Unknown`]: enum.CommandError.html#variant.Unknown
     /// [`WrongPassword`]: enum.CommandError.html#variant.WrongPassword
-    fn get_password_safe(&self, user_pin: &str) -> Result<PasswordSafe<'_>, Error>;
+    fn get_password_safe(&mut self, user_pin: &str) -> Result<PasswordSafe<'_>, Error>;
 }
 
 fn get_password_safe<'a>(
@@ -148,7 +149,7 @@ impl<'a> PasswordSafe<'a> {
     /// # use nitrokey::Error;
     ///
     /// # fn try_main() -> Result<(), Error> {
-    /// let device = nitrokey::connect()?;
+    /// let mut device = nitrokey::connect()?;
     /// let pws = device.get_password_safe("123456")?;
     /// pws.get_slot_status()?.iter().enumerate().for_each(|(slot, programmed)| {
     ///     let status = match *programmed {
@@ -193,7 +194,7 @@ impl<'a> PasswordSafe<'a> {
     /// # use nitrokey::Error;
     ///
     /// # fn try_main() -> Result<(), Error> {
-    /// let device = nitrokey::connect()?;
+    /// let mut device = nitrokey::connect()?;
     /// match device.get_password_safe("123456") {
     ///     Ok(pws) => {
     ///         let name = pws.get_slot_name(0)?;
@@ -201,7 +202,7 @@ impl<'a> PasswordSafe<'a> {
     ///         let password = pws.get_slot_login(0)?;
     ///         println!("Credentials for {}: login {}, password {}", name, login, password);
     ///     },
-    ///     Err(err) => println!("Could not open the password safe: {}", err),
+    ///     Err(err) => eprintln!("Could not open the password safe: {}", err),
     /// };
     /// #     Ok(())
     /// # }
@@ -230,7 +231,7 @@ impl<'a> PasswordSafe<'a> {
     /// # use nitrokey::Error;
     ///
     /// # fn try_main() -> Result<(), Error> {
-    /// let device = nitrokey::connect()?;
+    /// let mut device = nitrokey::connect()?;
     /// let pws = device.get_password_safe("123456")?;
     /// let name = pws.get_slot_name(0)?;
     /// let login = pws.get_slot_login(0)?;
@@ -263,7 +264,7 @@ impl<'a> PasswordSafe<'a> {
     /// # use nitrokey::Error;
     ///
     /// # fn try_main() -> Result<(), Error> {
-    /// let device = nitrokey::connect()?;
+    /// let mut device = nitrokey::connect()?;
     /// let pws = device.get_password_safe("123456")?;
     /// let name = pws.get_slot_name(0)?;
     /// let login = pws.get_slot_login(0)?;
@@ -294,7 +295,7 @@ impl<'a> PasswordSafe<'a> {
     /// # use nitrokey::Error;
     ///
     /// # fn try_main() -> Result<(), Error> {
-    /// let device = nitrokey::connect()?;
+    /// let mut device = nitrokey::connect()?;
     /// let pws = device.get_password_safe("123456")?;
     /// let name = pws.get_slot_name(0)?;
     /// let login = pws.get_slot_login(0)?;
@@ -307,7 +308,7 @@ impl<'a> PasswordSafe<'a> {
     /// [`InvalidSlot`]: enum.LibraryError.html#variant.InvalidSlot
     /// [`InvalidString`]: enum.LibraryError.html#variant.InvalidString
     pub fn write_slot(
-        &self,
+        &mut self,
         slot: u8,
         name: &str,
         login: &str,
@@ -340,18 +341,18 @@ impl<'a> PasswordSafe<'a> {
     /// # use nitrokey::Error;
     ///
     /// # fn try_main() -> Result<(), Error> {
-    /// let device = nitrokey::connect()?;
-    /// let pws = device.get_password_safe("123456")?;
+    /// let mut device = nitrokey::connect()?;
+    /// let mut pws = device.get_password_safe("123456")?;
     /// match pws.erase_slot(0) {
     ///     Ok(()) => println!("Erased slot 0."),
-    ///     Err(err) => println!("Could not erase slot 0: {}", err),
+    ///     Err(err) => eprintln!("Could not erase slot 0: {}", err),
     /// };
     /// #     Ok(())
     /// # }
     /// ```
     ///
     /// [`InvalidSlot`]: enum.LibraryError.html#variant.InvalidSlot
-    pub fn erase_slot(&self, slot: u8) -> Result<(), Error> {
+    pub fn erase_slot(&mut self, slot: u8) -> Result<(), Error> {
         get_command_result(unsafe { nitrokey_sys::NK_erase_password_safe_slot(slot) })
     }
 }
@@ -364,19 +365,19 @@ impl<'a> Drop for PasswordSafe<'a> {
 }
 
 impl GetPasswordSafe for Pro {
-    fn get_password_safe(&self, user_pin: &str) -> Result<PasswordSafe<'_>, Error> {
+    fn get_password_safe(&mut self, user_pin: &str) -> Result<PasswordSafe<'_>, Error> {
         get_password_safe(self, user_pin)
     }
 }
 
 impl GetPasswordSafe for Storage {
-    fn get_password_safe(&self, user_pin: &str) -> Result<PasswordSafe<'_>, Error> {
+    fn get_password_safe(&mut self, user_pin: &str) -> Result<PasswordSafe<'_>, Error> {
         get_password_safe(self, user_pin)
     }
 }
 
 impl GetPasswordSafe for DeviceWrapper {
-    fn get_password_safe(&self, user_pin: &str) -> Result<PasswordSafe<'_>, Error> {
+    fn get_password_safe(&mut self, user_pin: &str) -> Result<PasswordSafe<'_>, Error> {
         get_password_safe(self, user_pin)
     }
 }
diff --git a/nitrokey/src/util.rs b/nitrokey/src/util.rs
index b7e8cd3..fdb73c3 100644
--- a/nitrokey/src/util.rs
+++ b/nitrokey/src/util.rs
@@ -53,6 +53,10 @@ pub fn result_from_string(ptr: *const c_char) -> Result<String, Error> {
     }
 }
 
+pub fn result_or_error<T>(value: T) -> Result<T, Error> {
+    get_last_result().and(Ok(value))
+}
+
 pub fn get_command_result(value: c_int) -> Result<(), Error> {
     if value == 0 {
         Ok(())
diff --git a/nitrokey/tests/device.rs b/nitrokey/tests/device.rs
index c790049..5c52024 100644
--- a/nitrokey/tests/device.rs
+++ b/nitrokey/tests/device.rs
@@ -10,11 +10,10 @@ use std::{thread, time};
 use nitrokey::{
     Authenticate, CommandError, CommunicationError, Config, ConfigureOtp, Device, Error,
     GenerateOtp, GetPasswordSafe, LibraryError, OtpMode, OtpSlotData, Storage, VolumeMode,
+    DEFAULT_ADMIN_PIN, DEFAULT_USER_PIN,
 };
 use nitrokey_test::test as test_device;
 
-use crate::util::{ADMIN_PASSWORD, USER_PASSWORD};
-
 static ADMIN_NEW_PASSWORD: &str = "1234567890";
 static UPDATE_PIN: &str = "12345678";
 static UPDATE_NEW_PIN: &str = "87654321";
@@ -55,9 +54,9 @@ fn connect_pro(device: Pro) {
     assert_eq!(device.get_model(), nitrokey::Model::Pro);
     drop(device);
 
-    assert!(nitrokey::connect().is_ok());
-    assert!(nitrokey::connect_model(nitrokey::Model::Pro).is_ok());
-    assert!(nitrokey::Pro::connect().is_ok());
+    assert_any_ok!(nitrokey::connect());
+    assert_any_ok!(nitrokey::connect_model(nitrokey::Model::Pro));
+    assert_any_ok!(nitrokey::Pro::connect());
 }
 
 #[test_device]
@@ -65,9 +64,9 @@ fn connect_storage(device: Storage) {
     assert_eq!(device.get_model(), nitrokey::Model::Storage);
     drop(device);
 
-    assert!(nitrokey::connect().is_ok());
-    assert!(nitrokey::connect_model(nitrokey::Model::Storage).is_ok());
-    assert!(nitrokey::Storage::connect().is_ok());
+    assert_any_ok!(nitrokey::connect());
+    assert_any_ok!(nitrokey::connect_model(nitrokey::Model::Storage));
+    assert_any_ok!(nitrokey::Storage::connect());
 }
 
 fn assert_empty_serial_number() {
@@ -87,36 +86,34 @@ fn disconnect(device: DeviceWrapper) {
 
 #[test_device]
 fn get_serial_number(device: DeviceWrapper) {
-    let result = device.get_serial_number();
-    assert!(result.is_ok());
-    let serial_number = result.unwrap();
+    let serial_number = unwrap_ok!(device.get_serial_number());
     assert!(serial_number.is_ascii());
     assert!(serial_number.chars().all(|c| c.is_ascii_hexdigit()));
 }
 #[test_device]
 fn get_firmware_version(device: Pro) {
-    assert_eq!(0, device.get_major_firmware_version());
-    let minor = device.get_minor_firmware_version();
-    assert!(minor > 0);
+    let version = unwrap_ok!(device.get_firmware_version());
+    assert_eq!(0, version.major);
+    assert!(version.minor > 0);
 }
 
 fn admin_retry<T: Authenticate + Device>(device: T, suffix: &str, count: u8) -> T {
-    let result = device.authenticate_admin(&(ADMIN_PASSWORD.to_owned() + suffix));
+    let result = device.authenticate_admin(&(DEFAULT_ADMIN_PIN.to_owned() + suffix));
     let device = match result {
         Ok(admin) => admin.device(),
         Err((device, _)) => device,
     };
-    assert_eq!(count, device.get_admin_retry_count());
+    assert_ok!(count, device.get_admin_retry_count());
     return device;
 }
 
 fn user_retry<T: Authenticate + Device>(device: T, suffix: &str, count: u8) -> T {
-    let result = device.authenticate_user(&(USER_PASSWORD.to_owned() + suffix));
+    let result = device.authenticate_user(&(DEFAULT_USER_PIN.to_owned() + suffix));
     let device = match result {
         Ok(admin) => admin.device(),
         Err((device, _)) => device,
     };
-    assert_eq!(count, device.get_user_retry_count());
+    assert_ok!(count, device.get_user_retry_count());
     return device;
 }
 
@@ -135,7 +132,7 @@ fn get_retry_count(device: DeviceWrapper) {
 
 #[test_device]
 fn config(device: DeviceWrapper) {
-    let admin = device.authenticate_admin(ADMIN_PASSWORD).unwrap();
+    let mut admin = unwrap_ok!(device.authenticate_admin(DEFAULT_ADMIN_PIN));
 
     let config = Config::new(None, None, None, true);
     assert_ok!((), admin.write_config(config));
@@ -155,53 +152,67 @@ fn config(device: DeviceWrapper) {
 
 #[test_device]
 fn change_user_pin(device: DeviceWrapper) {
-    let device = device.authenticate_user(USER_PASSWORD).unwrap().device();
+    let device = device.authenticate_user(DEFAULT_USER_PIN).unwrap().device();
     let device = device.authenticate_user(USER_NEW_PASSWORD).unwrap_err().0;
 
-    assert_ok!((), device.change_user_pin(USER_PASSWORD, USER_NEW_PASSWORD));
+    let mut device = device;
+    assert_ok!(
+        (),
+        device.change_user_pin(DEFAULT_USER_PIN, USER_NEW_PASSWORD)
+    );
 
-    let device = device.authenticate_user(USER_PASSWORD).unwrap_err().0;
+    let device = device.authenticate_user(DEFAULT_USER_PIN).unwrap_err().0;
     let device = device
         .authenticate_user(USER_NEW_PASSWORD)
         .unwrap()
         .device();
 
-    let result = device.change_user_pin(USER_PASSWORD, USER_PASSWORD);
+    let mut device = device;
+    let result = device.change_user_pin(DEFAULT_USER_PIN, DEFAULT_USER_PIN);
     assert_cmd_err!(CommandError::WrongPassword, result);
 
-    assert_ok!((), device.change_user_pin(USER_NEW_PASSWORD, USER_PASSWORD));
+    assert_ok!(
+        (),
+        device.change_user_pin(USER_NEW_PASSWORD, DEFAULT_USER_PIN)
+    );
 
-    let device = device.authenticate_user(USER_PASSWORD).unwrap().device();
+    let device = device.authenticate_user(DEFAULT_USER_PIN).unwrap().device();
     assert!(device.authenticate_user(USER_NEW_PASSWORD).is_err());
 }
 
 #[test_device]
 fn change_admin_pin(device: DeviceWrapper) {
-    let device = device.authenticate_admin(ADMIN_PASSWORD).unwrap().device();
-    let device = device.authenticate_admin(ADMIN_NEW_PASSWORD).unwrap_err().0;
+    let device = device
+        .authenticate_admin(DEFAULT_ADMIN_PIN)
+        .unwrap()
+        .device();
+    let mut device = device.authenticate_admin(ADMIN_NEW_PASSWORD).unwrap_err().0;
 
     assert_ok!(
         (),
-        device.change_admin_pin(ADMIN_PASSWORD, ADMIN_NEW_PASSWORD)
+        device.change_admin_pin(DEFAULT_ADMIN_PIN, ADMIN_NEW_PASSWORD)
     );
 
-    let device = device.authenticate_admin(ADMIN_PASSWORD).unwrap_err().0;
-    let device = device
+    let device = device.authenticate_admin(DEFAULT_ADMIN_PIN).unwrap_err().0;
+    let mut device = device
         .authenticate_admin(ADMIN_NEW_PASSWORD)
         .unwrap()
         .device();
 
     assert_cmd_err!(
         CommandError::WrongPassword,
-        device.change_admin_pin(ADMIN_PASSWORD, ADMIN_PASSWORD)
+        device.change_admin_pin(DEFAULT_ADMIN_PIN, DEFAULT_ADMIN_PIN)
     );
 
     assert_ok!(
         (),
-        device.change_admin_pin(ADMIN_NEW_PASSWORD, ADMIN_PASSWORD)
+        device.change_admin_pin(ADMIN_NEW_PASSWORD, DEFAULT_ADMIN_PIN)
     );
 
-    let device = device.authenticate_admin(ADMIN_PASSWORD).unwrap().device();
+    let device = device
+        .authenticate_admin(DEFAULT_ADMIN_PIN)
+        .unwrap()
+        .device();
     device.authenticate_admin(ADMIN_NEW_PASSWORD).unwrap_err();
 }
 
@@ -222,63 +233,85 @@ where
 
 #[test_device]
 fn unlock_user_pin(device: DeviceWrapper) {
-    let device = device.authenticate_user(USER_PASSWORD).unwrap().device();
-    assert_ok!((), device.unlock_user_pin(ADMIN_PASSWORD, USER_PASSWORD));
+    let mut device = device.authenticate_user(DEFAULT_USER_PIN).unwrap().device();
+    assert_ok!(
+        (),
+        device.unlock_user_pin(DEFAULT_ADMIN_PIN, DEFAULT_USER_PIN)
+    );
     assert_cmd_err!(
         CommandError::WrongPassword,
-        device.unlock_user_pin(USER_PASSWORD, USER_PASSWORD)
+        device.unlock_user_pin(DEFAULT_USER_PIN, DEFAULT_USER_PIN)
     );
 
     // block user PIN
-    let wrong_password = USER_PASSWORD.to_owned() + "foo";
+    let wrong_password = DEFAULT_USER_PIN.to_owned() + "foo";
     let device = require_failed_user_login(device, &wrong_password, CommandError::WrongPassword);
     let device = require_failed_user_login(device, &wrong_password, CommandError::WrongPassword);
     let device = require_failed_user_login(device, &wrong_password, CommandError::WrongPassword);
-    let device = require_failed_user_login(device, USER_PASSWORD, CommandError::WrongPassword);
+    let mut device =
+        require_failed_user_login(device, DEFAULT_USER_PIN, CommandError::WrongPassword);
 
     // unblock with current PIN
     assert_cmd_err!(
         CommandError::WrongPassword,
-        device.unlock_user_pin(USER_PASSWORD, USER_PASSWORD)
+        device.unlock_user_pin(DEFAULT_USER_PIN, DEFAULT_USER_PIN)
     );
-    assert_ok!((), device.unlock_user_pin(ADMIN_PASSWORD, USER_PASSWORD));
-    let device = device.authenticate_user(USER_PASSWORD).unwrap().device();
+    assert_ok!(
+        (),
+        device.unlock_user_pin(DEFAULT_ADMIN_PIN, DEFAULT_USER_PIN)
+    );
+    let device = device.authenticate_user(DEFAULT_USER_PIN).unwrap().device();
 
     // block user PIN
     let device = require_failed_user_login(device, &wrong_password, CommandError::WrongPassword);
     let device = require_failed_user_login(device, &wrong_password, CommandError::WrongPassword);
     let device = require_failed_user_login(device, &wrong_password, CommandError::WrongPassword);
-    let device = require_failed_user_login(device, USER_PASSWORD, CommandError::WrongPassword);
+    let mut device =
+        require_failed_user_login(device, DEFAULT_USER_PIN, CommandError::WrongPassword);
 
     // unblock with new PIN
     assert_cmd_err!(
         CommandError::WrongPassword,
-        device.unlock_user_pin(USER_PASSWORD, USER_PASSWORD)
+        device.unlock_user_pin(DEFAULT_USER_PIN, DEFAULT_USER_PIN)
     );
     assert_ok!(
         (),
-        device.unlock_user_pin(ADMIN_PASSWORD, USER_NEW_PASSWORD)
+        device.unlock_user_pin(DEFAULT_ADMIN_PIN, USER_NEW_PASSWORD)
     );
 
     // reset user PIN
-    assert_ok!((), device.change_user_pin(USER_NEW_PASSWORD, USER_PASSWORD));
+    assert_ok!(
+        (),
+        device.change_user_pin(USER_NEW_PASSWORD, DEFAULT_USER_PIN)
+    );
+}
+
+fn assert_utf8_err_or_ne(left: &str, right: Result<String, Error>) {
+    match right {
+        Ok(s) => assert_ne!(left.to_string(), s),
+        Err(Error::Utf8Error(_)) => {}
+        Err(err) => panic!("Expected Utf8Error, got {}!", err),
+    }
 }
 
 #[test_device]
 fn factory_reset(device: DeviceWrapper) {
-    let admin = device.authenticate_admin(ADMIN_PASSWORD).unwrap();
+    let mut admin = unwrap_ok!(device.authenticate_admin(DEFAULT_ADMIN_PIN));
     let otp_data = OtpSlotData::new(1, "test", "0123468790", OtpMode::SixDigits);
     assert_ok!((), admin.write_totp_slot(otp_data, 30));
 
-    let device = admin.device();
-    let pws = device.get_password_safe(USER_PASSWORD).unwrap();
+    let mut device = admin.device();
+    let mut pws = unwrap_ok!(device.get_password_safe(DEFAULT_USER_PIN));
     assert_ok!((), pws.write_slot(0, "test", "testlogin", "testpw"));
     drop(pws);
 
-    assert_ok!((), device.change_user_pin(USER_PASSWORD, USER_NEW_PASSWORD));
     assert_ok!(
         (),
-        device.change_admin_pin(ADMIN_PASSWORD, ADMIN_NEW_PASSWORD)
+        device.change_user_pin(DEFAULT_USER_PIN, USER_NEW_PASSWORD)
+    );
+    assert_ok!(
+        (),
+        device.change_admin_pin(DEFAULT_ADMIN_PIN, ADMIN_NEW_PASSWORD)
     );
 
     assert_cmd_err!(
@@ -287,46 +320,55 @@ fn factory_reset(device: DeviceWrapper) {
     );
     assert_cmd_err!(
         CommandError::WrongPassword,
-        device.factory_reset(ADMIN_PASSWORD)
+        device.factory_reset(DEFAULT_ADMIN_PIN)
     );
     assert_ok!((), device.factory_reset(ADMIN_NEW_PASSWORD));
 
-    let device = device.authenticate_admin(ADMIN_PASSWORD).unwrap().device();
+    let device = device
+        .authenticate_admin(DEFAULT_ADMIN_PIN)
+        .unwrap()
+        .device();
 
-    let user = device.authenticate_user(USER_PASSWORD).unwrap();
+    let user = unwrap_ok!(device.authenticate_user(DEFAULT_USER_PIN));
     assert_cmd_err!(CommandError::SlotNotProgrammed, user.get_totp_slot_name(1));
 
-    let device = user.device();
-    let pws = device.get_password_safe(USER_PASSWORD).unwrap();
-    assert_ne!("test".to_string(), pws.get_slot_name(0).unwrap());
-    assert_ne!("testlogin".to_string(), pws.get_slot_login(0).unwrap());
-    assert_ne!("testpw".to_string(), pws.get_slot_password(0).unwrap());
+    let mut device = user.device();
+    let pws = unwrap_ok!(device.get_password_safe(DEFAULT_USER_PIN));
+    assert_utf8_err_or_ne("test", pws.get_slot_name(0));
+    assert_utf8_err_or_ne("testlogin", pws.get_slot_login(0));
+    assert_utf8_err_or_ne("testpw", pws.get_slot_password(0));
+    drop(pws);
 
-    assert_ok!((), device.build_aes_key(ADMIN_PASSWORD));
+    assert_ok!((), device.build_aes_key(DEFAULT_ADMIN_PIN));
 }
 
 #[test_device]
 fn build_aes_key(device: DeviceWrapper) {
-    let pws = device.get_password_safe(USER_PASSWORD).unwrap();
+    let mut device = device;
+    let mut pws = unwrap_ok!(device.get_password_safe(DEFAULT_USER_PIN));
     assert_ok!((), pws.write_slot(0, "test", "testlogin", "testpw"));
     drop(pws);
 
     assert_cmd_err!(
         CommandError::WrongPassword,
-        device.build_aes_key(USER_PASSWORD)
+        device.build_aes_key(DEFAULT_USER_PIN)
     );
-    assert_ok!((), device.build_aes_key(ADMIN_PASSWORD));
+    assert_ok!((), device.build_aes_key(DEFAULT_ADMIN_PIN));
 
-    let device = device.authenticate_admin(ADMIN_PASSWORD).unwrap().device();
+    let mut device = device
+        .authenticate_admin(DEFAULT_ADMIN_PIN)
+        .unwrap()
+        .device();
 
-    let pws = device.get_password_safe(USER_PASSWORD).unwrap();
-    assert_ne!("test".to_string(), pws.get_slot_name(0).unwrap());
-    assert_ne!("testlogin".to_string(), pws.get_slot_login(0).unwrap());
-    assert_ne!("testpw".to_string(), pws.get_slot_password(0).unwrap());
+    let pws = unwrap_ok!(device.get_password_safe(DEFAULT_USER_PIN));
+    assert_utf8_err_or_ne("test", pws.get_slot_name(0));
+    assert_utf8_err_or_ne("testlogin", pws.get_slot_login(0));
+    assert_utf8_err_or_ne("testpw", pws.get_slot_password(0));
 }
 
 #[test_device]
 fn change_update_pin(device: Storage) {
+    let mut device = device;
     assert_cmd_err!(
         CommandError::WrongPassword,
         device.change_update_pin(UPDATE_NEW_PIN, UPDATE_PIN)
@@ -337,6 +379,7 @@ fn change_update_pin(device: Storage) {
 
 #[test_device]
 fn encrypted_volume(device: Storage) {
+    let mut device = device;
     assert_ok!((), device.lock());
 
     assert_eq!(1, count_nitrokey_block_devices());
@@ -347,7 +390,7 @@ fn encrypted_volume(device: Storage) {
         device.enable_encrypted_volume("123")
     );
     assert_eq!(1, count_nitrokey_block_devices());
-    assert_ok!((), device.enable_encrypted_volume(USER_PASSWORD));
+    assert_ok!((), device.enable_encrypted_volume(DEFAULT_USER_PIN));
     assert_eq!(2, count_nitrokey_block_devices());
     assert_ok!((), device.disable_encrypted_volume());
     assert_eq!(1, count_nitrokey_block_devices());
@@ -355,13 +398,14 @@ fn encrypted_volume(device: Storage) {
 
 #[test_device]
 fn hidden_volume(device: Storage) {
+    let mut device = device;
     assert_ok!((), device.lock());
 
     assert_eq!(1, count_nitrokey_block_devices());
     assert_ok!((), device.disable_hidden_volume());
     assert_eq!(1, count_nitrokey_block_devices());
 
-    assert_ok!((), device.enable_encrypted_volume(USER_PASSWORD));
+    assert_ok!((), device.enable_encrypted_volume(DEFAULT_USER_PIN));
     assert_eq!(2, count_nitrokey_block_devices());
 
     // TODO: why this error code?
@@ -390,51 +434,85 @@ fn hidden_volume(device: Storage) {
 
 #[test_device]
 fn lock(device: Storage) {
-    assert_ok!((), device.enable_encrypted_volume(USER_PASSWORD));
+    let mut device = device;
+    assert_ok!((), device.enable_encrypted_volume(DEFAULT_USER_PIN));
     assert_ok!((), device.lock());
     assert_eq!(1, count_nitrokey_block_devices());
 }
 
 #[test_device]
+fn set_encrypted_volume_mode(device: Storage) {
+    // This test case does not check the device status as the command only works with firmware
+    // version 0.49.  For later versions, it does not do anything and always returns Ok(()).
+    let mut device = device;
+
+    assert_ok!(
+        (),
+        device.set_encrypted_volume_mode(DEFAULT_ADMIN_PIN, VolumeMode::ReadOnly)
+    );
+
+    // TODO: re-enable once the password is checked in the firmware
+    // assert_cmd_err!(
+    //     CommandError::WrongPassword,
+    //     device.set_encrypted_volume_mode(DEFAULT_USER_PIN, VolumeMode::ReadOnly)
+    // );
+
+    assert_ok!(
+        (),
+        device.set_encrypted_volume_mode(DEFAULT_ADMIN_PIN, VolumeMode::ReadOnly)
+    );
+    assert_ok!(
+        (),
+        device.set_encrypted_volume_mode(DEFAULT_ADMIN_PIN, VolumeMode::ReadWrite)
+    );
+    assert_ok!(
+        (),
+        device.set_encrypted_volume_mode(DEFAULT_ADMIN_PIN, VolumeMode::ReadOnly)
+    );
+}
+
+#[test_device]
 fn set_unencrypted_volume_mode(device: Storage) {
     fn assert_mode(device: &Storage, mode: VolumeMode) {
-        let status = device.get_status();
-        assert!(status.is_ok());
+        let status = unwrap_ok!(device.get_status());
         assert_eq!(
-            status.unwrap().unencrypted_volume.read_only,
+            status.unencrypted_volume.read_only,
             mode == VolumeMode::ReadOnly
         );
     }
 
-    fn assert_success(device: &Storage, mode: VolumeMode) {
-        assert_ok!((), device.set_unencrypted_volume_mode(ADMIN_PASSWORD, mode));
+    fn assert_success(device: &mut Storage, mode: VolumeMode) {
+        assert_ok!(
+            (),
+            device.set_unencrypted_volume_mode(DEFAULT_ADMIN_PIN, mode)
+        );
         assert_mode(&device, mode);
     }
 
-    assert_success(&device, VolumeMode::ReadOnly);
+    let mut device = device;
+    assert_success(&mut device, VolumeMode::ReadOnly);
 
     assert_cmd_err!(
         CommandError::WrongPassword,
-        device.set_unencrypted_volume_mode(USER_PASSWORD, VolumeMode::ReadOnly)
+        device.set_unencrypted_volume_mode(DEFAULT_USER_PIN, VolumeMode::ReadOnly)
     );
     assert_mode(&device, VolumeMode::ReadOnly);
 
-    assert_success(&device, VolumeMode::ReadWrite);
-    assert_success(&device, VolumeMode::ReadWrite);
-    assert_success(&device, VolumeMode::ReadOnly);
+    assert_success(&mut device, VolumeMode::ReadWrite);
+    assert_success(&mut device, VolumeMode::ReadWrite);
+    assert_success(&mut device, VolumeMode::ReadOnly);
 }
 
 #[test_device]
 fn get_storage_status(device: Storage) {
-    let status = device.get_status().unwrap();
-
+    let status = unwrap_ok!(device.get_status());
     assert!(status.serial_number_sd_card > 0);
     assert!(status.serial_number_smart_card > 0);
 }
 
 #[test_device]
 fn get_production_info(device: Storage) {
-    let info = device.get_production_info().unwrap();
+    let info = unwrap_ok!(device.get_production_info());
     assert_eq!(0, info.firmware_version.major);
     assert!(info.firmware_version.minor != 0);
     assert!(info.serial_number_cpu != 0);
@@ -447,43 +525,45 @@ fn get_production_info(device: Storage) {
     assert!(info.sd_card.oem != 0);
     assert!(info.sd_card.manufacturer != 0);
 
-    let status = device.get_status().unwrap();
+    let status = unwrap_ok!(device.get_status());
     assert_eq!(status.firmware_version, info.firmware_version);
     assert_eq!(status.serial_number_sd_card, info.sd_card.serial_number);
 }
 
 #[test_device]
 fn clear_new_sd_card_warning(device: Storage) {
-    assert_ok!((), device.factory_reset(ADMIN_PASSWORD));
+    let mut device = device;
+    assert_ok!((), device.factory_reset(DEFAULT_ADMIN_PIN));
     thread::sleep(time::Duration::from_secs(3));
-    assert_ok!((), device.build_aes_key(ADMIN_PASSWORD));
+    assert_ok!((), device.build_aes_key(DEFAULT_ADMIN_PIN));
 
     // We have to perform an SD card operation to reset the new_sd_card_found field
     assert_ok!((), device.lock());
 
-    let status = device.get_status().unwrap();
+    let status = unwrap_ok!(device.get_status());
     assert!(status.new_sd_card_found);
 
-    assert_ok!((), device.clear_new_sd_card_warning(ADMIN_PASSWORD));
+    assert_ok!((), device.clear_new_sd_card_warning(DEFAULT_ADMIN_PIN));
 
-    let status = device.get_status().unwrap();
+    let status = unwrap_ok!(device.get_status());
     assert!(!status.new_sd_card_found);
 }
 
 #[test_device]
 fn export_firmware(device: Storage) {
+    let mut device = device;
     assert_cmd_err!(
         CommandError::WrongPassword,
         device.export_firmware("someadminpn")
     );
-    assert_ok!((), device.export_firmware(ADMIN_PASSWORD));
+    assert_ok!((), device.export_firmware(DEFAULT_ADMIN_PIN));
     assert_ok!(
         (),
-        device.set_unencrypted_volume_mode(ADMIN_PASSWORD, VolumeMode::ReadWrite)
+        device.set_unencrypted_volume_mode(DEFAULT_ADMIN_PIN, VolumeMode::ReadWrite)
     );
-    assert_ok!((), device.export_firmware(ADMIN_PASSWORD));
+    assert_ok!((), device.export_firmware(DEFAULT_ADMIN_PIN));
     assert_ok!(
         (),
-        device.set_unencrypted_volume_mode(ADMIN_PASSWORD, VolumeMode::ReadOnly)
+        device.set_unencrypted_volume_mode(DEFAULT_ADMIN_PIN, VolumeMode::ReadOnly)
     );
 }
diff --git a/nitrokey/tests/lib.rs b/nitrokey/tests/lib.rs
index 697024d..8ab75f6 100644
--- a/nitrokey/tests/lib.rs
+++ b/nitrokey/tests/lib.rs
@@ -1,9 +1,11 @@
 // Copyright (C) 2019 Robin Krahl <robin.krahl@ireas.org>
 // SPDX-License-Identifier: MIT
 
+mod util;
+
 #[test]
 fn get_library_version() {
-    let version = nitrokey::get_library_version().unwrap();
+    let version = unwrap_ok!(nitrokey::get_library_version());
 
     assert!(version.git.is_empty() || version.git.starts_with("v"));
     assert!(version.major > 0);
diff --git a/nitrokey/tests/otp.rs b/nitrokey/tests/otp.rs
index e424673..c0bbecf 100644
--- a/nitrokey/tests/otp.rs
+++ b/nitrokey/tests/otp.rs
@@ -4,16 +4,14 @@
 mod util;
 
 use std::fmt::Debug;
-use std::ops::Deref;
+use std::ops::DerefMut;
 
 use nitrokey::{
     Admin, Authenticate, CommandError, Config, ConfigureOtp, Device, GenerateOtp, LibraryError,
-    OtpMode, OtpSlotData,
+    OtpMode, OtpSlotData, DEFAULT_ADMIN_PIN, DEFAULT_USER_PIN,
 };
 use nitrokey_test::test as test_device;
 
-use crate::util::{ADMIN_PASSWORD, USER_PASSWORD};
-
 // test suite according to RFC 4226, Appendix D
 static HOTP_SECRET: &str = "3132333435363738393031323334353637383930";
 static HOTP_CODES: &[&str] = &[
@@ -43,27 +41,25 @@ where
     T: Device,
     (T, nitrokey::Error): Debug,
 {
-    device
-        .authenticate_admin(ADMIN_PASSWORD)
-        .expect("Could not login as admin.")
+    unwrap_ok!(device.authenticate_admin(DEFAULT_ADMIN_PIN))
 }
 
-fn configure_hotp(admin: &ConfigureOtp, counter: u8) {
+fn configure_hotp(admin: &mut ConfigureOtp, counter: u8) {
     let slot_data = OtpSlotData::new(1, "test-hotp", HOTP_SECRET, OtpMode::SixDigits);
     assert_ok!((), admin.write_hotp_slot(slot_data, counter.into()));
 }
 
-fn check_hotp_codes(device: &GenerateOtp, offset: u8) {
+fn check_hotp_codes(device: &mut GenerateOtp, offset: u8) {
     HOTP_CODES.iter().enumerate().for_each(|(i, code)| {
         if i >= offset as usize {
-            let result = device.get_hotp_code(1);
-            assert_eq!(code, &result.unwrap());
+            assert_ok!(code.to_string(), device.get_hotp_code(1));
         }
     });
 }
 
 #[test_device]
 fn set_time(device: DeviceWrapper) {
+    let mut device = device;
     assert_ok!((), device.set_time(1546385382, true));
     assert_ok!((), device.set_time(1546385392, false));
     assert_cmd_err!(CommandError::Timestamp, device.set_time(1546385292, false));
@@ -72,49 +68,47 @@ fn set_time(device: DeviceWrapper) {
 
 #[test_device]
 fn hotp_no_pin(device: DeviceWrapper) {
-    let admin = make_admin_test_device(device);
+    let mut admin = make_admin_test_device(device);
     let config = Config::new(None, None, None, false);
     assert_ok!((), admin.write_config(config));
 
-    configure_hotp(&admin, 0);
-    check_hotp_codes(admin.deref(), 0);
+    configure_hotp(&mut admin, 0);
+    check_hotp_codes(admin.deref_mut(), 0);
 
-    configure_hotp(&admin, 5);
-    check_hotp_codes(admin.deref(), 5);
+    configure_hotp(&mut admin, 5);
+    check_hotp_codes(admin.deref_mut(), 5);
 
-    configure_hotp(&admin, 0);
-    check_hotp_codes(&admin.device(), 0);
+    configure_hotp(&mut admin, 0);
+    check_hotp_codes(&mut admin.device(), 0);
 }
 
 #[test_device]
 fn hotp_pin(device: DeviceWrapper) {
-    let admin = make_admin_test_device(device);
+    let mut admin = make_admin_test_device(device);
     let config = Config::new(None, None, None, true);
     assert_ok!((), admin.write_config(config));
 
-    configure_hotp(&admin, 0);
-    let user = admin.device().authenticate_user(USER_PASSWORD).unwrap();
-    check_hotp_codes(&user, 0);
+    configure_hotp(&mut admin, 0);
+    let mut user = unwrap_ok!(admin.device().authenticate_user(DEFAULT_USER_PIN));
+    check_hotp_codes(&mut user, 0);
 
     assert_cmd_err!(CommandError::NotAuthorized, user.device().get_hotp_code(1));
 }
 
 #[test_device]
 fn hotp_slot_name(device: DeviceWrapper) {
-    let admin = make_admin_test_device(device);
+    let mut admin = make_admin_test_device(device);
     let slot_data = OtpSlotData::new(1, "test-hotp", HOTP_SECRET, OtpMode::SixDigits);
     assert_ok!((), admin.write_hotp_slot(slot_data, 0));
 
     let device = admin.device();
-    let result = device.get_hotp_slot_name(1);
-    assert_eq!("test-hotp", result.unwrap());
-    let result = device.get_hotp_slot_name(4);
-    assert_lib_err!(LibraryError::InvalidSlot, result);
+    assert_ok!("test-hotp".to_string(), device.get_hotp_slot_name(1));
+    assert_lib_err!(LibraryError::InvalidSlot, device.get_hotp_slot_name(4));
 }
 
 #[test_device]
 fn hotp_error(device: DeviceWrapper) {
-    let admin = make_admin_test_device(device);
+    let mut admin = make_admin_test_device(device);
     let slot_data = OtpSlotData::new(1, "", HOTP_SECRET, OtpMode::SixDigits);
     assert_cmd_err!(CommandError::NoName, admin.write_hotp_slot(slot_data, 0));
     let slot_data = OtpSlotData::new(4, "test", HOTP_SECRET, OtpMode::SixDigits);
@@ -133,7 +127,7 @@ fn hotp_error(device: DeviceWrapper) {
 
 #[test_device]
 fn hotp_erase(device: DeviceWrapper) {
-    let admin = make_admin_test_device(device);
+    let mut admin = make_admin_test_device(device);
     let config = Config::new(None, None, None, false);
     assert_ok!((), admin.write_config(config));
     let slot_data = OtpSlotData::new(1, "test1", HOTP_SECRET, OtpMode::SixDigits);
@@ -143,22 +137,22 @@ fn hotp_erase(device: DeviceWrapper) {
 
     assert_ok!((), admin.erase_hotp_slot(1));
 
-    let device = admin.device();
+    let mut device = admin.device();
     let result = device.get_hotp_slot_name(1);
     assert_cmd_err!(CommandError::SlotNotProgrammed, result);
     let result = device.get_hotp_code(1);
     assert_cmd_err!(CommandError::SlotNotProgrammed, result);
 
-    assert_eq!("test2", device.get_hotp_slot_name(2).unwrap());
+    assert_ok!("test2".to_string(), device.get_hotp_slot_name(2));
 }
 
-fn configure_totp(admin: &ConfigureOtp, factor: u64) {
+fn configure_totp(admin: &mut ConfigureOtp, factor: u64) {
     let slot_data = OtpSlotData::new(1, "test-totp", TOTP_SECRET, OtpMode::EightDigits);
     let time_window = 30u64.checked_mul(factor).unwrap();
     assert_ok!((), admin.write_totp_slot(slot_data, time_window as u16));
 }
 
-fn check_totp_codes(device: &GenerateOtp, factor: u64, timestamp_size: TotpTimestampSize) {
+fn check_totp_codes(device: &mut GenerateOtp, factor: u64, timestamp_size: TotpTimestampSize) {
     for (base_time, codes) in TOTP_CODES {
         let time = base_time.checked_mul(factor).unwrap();
         let is_u64 = time > u32::max_value() as u64;
@@ -167,7 +161,7 @@ fn check_totp_codes(device: &GenerateOtp, factor: u64, timestamp_size: TotpTimes
         }
 
         assert_ok!((), device.set_time(time, true));
-        let code = device.get_totp_code(1).unwrap();
+        let code = unwrap_ok!(device.get_totp_code(1));
         assert!(
             code.contains(&code),
             "Generated TOTP code {} for {}, but expected one of {}",
@@ -180,49 +174,47 @@ fn check_totp_codes(device: &GenerateOtp, factor: u64, timestamp_size: TotpTimes
 
 #[test_device]
 fn totp_no_pin(device: DeviceWrapper) {
-    // TODO: this test may fail due to bad timing --> find solution
-    let admin = make_admin_test_device(device);
+    let mut admin = make_admin_test_device(device);
     let config = Config::new(None, None, None, false);
     assert_ok!((), admin.write_config(config));
 
-    configure_totp(&admin, 1);
-    check_totp_codes(admin.deref(), 1, TotpTimestampSize::U32);
+    configure_totp(&mut admin, 1);
+    check_totp_codes(admin.deref_mut(), 1, TotpTimestampSize::U32);
 
-    configure_totp(&admin, 2);
-    check_totp_codes(admin.deref(), 2, TotpTimestampSize::U32);
+    configure_totp(&mut admin, 2);
+    check_totp_codes(admin.deref_mut(), 2, TotpTimestampSize::U32);
 
-    configure_totp(&admin, 1);
-    check_totp_codes(&admin.device(), 1, TotpTimestampSize::U32);
+    configure_totp(&mut admin, 1);
+    check_totp_codes(&mut admin.device(), 1, TotpTimestampSize::U32);
 }
 
 #[test_device]
 // Nitrokey Storage does only support timestamps that fit in a 32-bit
 // unsigned integer, so don't test with it.
 fn totp_no_pin_64(device: Pro) {
-    let admin = make_admin_test_device(device);
+    let mut admin = make_admin_test_device(device);
     let config = Config::new(None, None, None, false);
     assert_ok!((), admin.write_config(config));
 
-    configure_totp(&admin, 1);
-    check_totp_codes(admin.deref(), 1, TotpTimestampSize::U64);
+    configure_totp(&mut admin, 1);
+    check_totp_codes(admin.deref_mut(), 1, TotpTimestampSize::U64);
 
-    configure_totp(&admin, 2);
-    check_totp_codes(admin.deref(), 2, TotpTimestampSize::U64);
+    configure_totp(&mut admin, 2);
+    check_totp_codes(admin.deref_mut(), 2, TotpTimestampSize::U64);
 
-    configure_totp(&admin, 1);
-    check_totp_codes(&admin.device(), 1, TotpTimestampSize::U64);
+    configure_totp(&mut admin, 1);
+    check_totp_codes(&mut admin.device(), 1, TotpTimestampSize::U64);
 }
 
 #[test_device]
 fn totp_pin(device: DeviceWrapper) {
-    // TODO: this test may fail due to bad timing --> find solution
-    let admin = make_admin_test_device(device);
+    let mut admin = make_admin_test_device(device);
     let config = Config::new(None, None, None, true);
     assert_ok!((), admin.write_config(config));
 
-    configure_totp(&admin, 1);
-    let user = admin.device().authenticate_user(USER_PASSWORD).unwrap();
-    check_totp_codes(&user, 1, TotpTimestampSize::U32);
+    configure_totp(&mut admin, 1);
+    let mut user = unwrap_ok!(admin.device().authenticate_user(DEFAULT_USER_PIN));
+    check_totp_codes(&mut user, 1, TotpTimestampSize::U32);
 
     assert_cmd_err!(CommandError::NotAuthorized, user.device().get_totp_code(1));
 }
@@ -230,20 +222,20 @@ fn totp_pin(device: DeviceWrapper) {
 #[test_device]
 // See comment for totp_no_pin_64.
 fn totp_pin_64(device: Pro) {
-    let admin = make_admin_test_device(device);
+    let mut admin = make_admin_test_device(device);
     let config = Config::new(None, None, None, true);
     assert_ok!((), admin.write_config(config));
 
-    configure_totp(&admin, 1);
-    let user = admin.device().authenticate_user(USER_PASSWORD).unwrap();
-    check_totp_codes(&user, 1, TotpTimestampSize::U64);
+    configure_totp(&mut admin, 1);
+    let mut user = unwrap_ok!(admin.device().authenticate_user(DEFAULT_USER_PIN));
+    check_totp_codes(&mut user, 1, TotpTimestampSize::U64);
 
     assert_cmd_err!(CommandError::NotAuthorized, user.device().get_totp_code(1));
 }
 
 #[test_device]
 fn totp_slot_name(device: DeviceWrapper) {
-    let admin = make_admin_test_device(device);
+    let mut admin = make_admin_test_device(device);
     let slot_data = OtpSlotData::new(1, "test-totp", TOTP_SECRET, OtpMode::EightDigits);
     assert_ok!((), admin.write_totp_slot(slot_data, 0));
 
@@ -256,7 +248,7 @@ fn totp_slot_name(device: DeviceWrapper) {
 
 #[test_device]
 fn totp_error(device: DeviceWrapper) {
-    let admin = make_admin_test_device(device);
+    let mut admin = make_admin_test_device(device);
     let slot_data = OtpSlotData::new(1, "", TOTP_SECRET, OtpMode::SixDigits);
     assert_cmd_err!(CommandError::NoName, admin.write_totp_slot(slot_data, 0));
     let slot_data = OtpSlotData::new(20, "test", TOTP_SECRET, OtpMode::SixDigits);
@@ -275,7 +267,7 @@ fn totp_error(device: DeviceWrapper) {
 
 #[test_device]
 fn totp_erase(device: DeviceWrapper) {
-    let admin = make_admin_test_device(device);
+    let mut admin = make_admin_test_device(device);
     let config = Config::new(None, None, None, false);
     assert_ok!((), admin.write_config(config));
     let slot_data = OtpSlotData::new(1, "test1", TOTP_SECRET, OtpMode::SixDigits);
@@ -291,5 +283,5 @@ fn totp_erase(device: DeviceWrapper) {
     let result = device.get_totp_code(1);
     assert_cmd_err!(CommandError::SlotNotProgrammed, result);
 
-    assert_eq!("test2", device.get_totp_slot_name(2).unwrap());
+    assert_ok!("test2".to_string(), device.get_totp_slot_name(2));
 }
diff --git a/nitrokey/tests/pws.rs b/nitrokey/tests/pws.rs
index df99e1c..b0e5abe 100644
--- a/nitrokey/tests/pws.rs
+++ b/nitrokey/tests/pws.rs
@@ -7,13 +7,12 @@ use std::ffi::CStr;
 
 use libc::{c_int, c_void, free};
 use nitrokey::{
-    CommandError, Device, Error, GetPasswordSafe, LibraryError, PasswordSafe, SLOT_COUNT,
+    CommandError, Device, Error, GetPasswordSafe, LibraryError, PasswordSafe, DEFAULT_ADMIN_PIN,
+    DEFAULT_USER_PIN, SLOT_COUNT,
 };
 use nitrokey_sys;
 use nitrokey_test::test as test_device;
 
-use crate::util::{ADMIN_PASSWORD, USER_PASSWORD};
-
 fn get_slot_name_direct(slot: u8) -> Result<String, Error> {
     let ptr = unsafe { nitrokey_sys::NK_get_password_safe_slot_name(slot) };
     if ptr.is_null() {
@@ -33,33 +32,35 @@ fn get_slot_name_direct(slot: u8) -> Result<String, Error> {
     }
 }
 
-fn get_pws<T>(device: &T) -> PasswordSafe
+fn get_pws<T>(device: &mut T) -> PasswordSafe
 where
     T: Device,
 {
-    device.get_password_safe(USER_PASSWORD).unwrap()
+    unwrap_ok!(device.get_password_safe(DEFAULT_USER_PIN))
 }
 
 #[test_device]
 fn enable(device: DeviceWrapper) {
+    let mut device = device;
     assert_cmd_err!(
         CommandError::WrongPassword,
-        device.get_password_safe(&(USER_PASSWORD.to_owned() + "123"))
+        device.get_password_safe(&(DEFAULT_USER_PIN.to_owned() + "123"))
     );
-    assert!(device.get_password_safe(USER_PASSWORD).is_ok());
+    assert_any_ok!(device.get_password_safe(DEFAULT_USER_PIN));
     assert_cmd_err!(
         CommandError::WrongPassword,
-        device.get_password_safe(ADMIN_PASSWORD)
+        device.get_password_safe(DEFAULT_ADMIN_PIN)
     );
-    assert!(device.get_password_safe(USER_PASSWORD).is_ok());
+    assert_any_ok!(device.get_password_safe(DEFAULT_USER_PIN));
 }
 
 #[test_device]
 fn drop(device: DeviceWrapper) {
+    let mut device = device;
     {
-        let pws = get_pws(&device);
+        let mut pws = get_pws(&mut device);
         assert_ok!((), pws.write_slot(1, "name", "login", "password"));
-        assert_eq!("name", pws.get_slot_name(1).unwrap());
+        assert_ok!("name".to_string(), pws.get_slot_name(1));
         let result = get_slot_name_direct(1);
         assert_ok!(String::from("name"), result);
     }
@@ -72,15 +73,16 @@ fn drop(device: DeviceWrapper) {
 
 #[test_device]
 fn get_status(device: DeviceWrapper) {
-    let pws = get_pws(&device);
+    let mut device = device;
+    let mut pws = get_pws(&mut device);
     for i in 0..SLOT_COUNT {
         assert_ok!((), pws.erase_slot(i));
     }
-    let status = pws.get_slot_status().unwrap();
+    let status = unwrap_ok!(pws.get_slot_status());
     assert_eq!(status, [false; SLOT_COUNT as usize]);
 
     assert_ok!((), pws.write_slot(1, "name", "login", "password"));
-    let status = pws.get_slot_status().unwrap();
+    let status = unwrap_ok!(pws.get_slot_status());
     for i in 0..SLOT_COUNT {
         assert_eq!(i == 1, status[i as usize]);
     }
@@ -88,17 +90,17 @@ fn get_status(device: DeviceWrapper) {
     for i in 0..SLOT_COUNT {
         assert_ok!((), pws.write_slot(i, "name", "login", "password"));
     }
-    let status = pws.get_slot_status().unwrap();
-    assert_eq!(status, [true; SLOT_COUNT as usize]);
+    assert_ok!([true; SLOT_COUNT as usize], pws.get_slot_status());
 }
 
 #[test_device]
 fn get_data(device: DeviceWrapper) {
-    let pws = get_pws(&device);
+    let mut device = device;
+    let mut pws = get_pws(&mut device);
     assert_ok!((), pws.write_slot(1, "name", "login", "password"));
-    assert_eq!("name", pws.get_slot_name(1).unwrap());
-    assert_eq!("login", pws.get_slot_login(1).unwrap());
-    assert_eq!("password", pws.get_slot_password(1).unwrap());
+    assert_ok!("name".to_string(), pws.get_slot_name(1));
+    assert_ok!("login".to_string(), pws.get_slot_login(1));
+    assert_ok!("password".to_string(), pws.get_slot_password(1));
 
     assert_ok!((), pws.erase_slot(1));
     assert_cmd_err!(CommandError::SlotNotProgrammed, pws.get_slot_name(1));
@@ -109,9 +111,9 @@ fn get_data(device: DeviceWrapper) {
     let login = "pär@test.com";
     let password = "'i3lJc[09?I:,[u7dWz9";
     assert_ok!((), pws.write_slot(1, name, login, password));
-    assert_eq!(name, pws.get_slot_name(1).unwrap());
-    assert_eq!(login, pws.get_slot_login(1).unwrap());
-    assert_eq!(password, pws.get_slot_password(1).unwrap());
+    assert_ok!(name.to_string(), pws.get_slot_name(1));
+    assert_ok!(login.to_string(), pws.get_slot_login(1));
+    assert_ok!(password.to_string(), pws.get_slot_password(1));
 
     assert_lib_err!(LibraryError::InvalidSlot, pws.get_slot_name(SLOT_COUNT));
     assert_lib_err!(LibraryError::InvalidSlot, pws.get_slot_login(SLOT_COUNT));
@@ -120,7 +122,8 @@ fn get_data(device: DeviceWrapper) {
 
 #[test_device]
 fn write(device: DeviceWrapper) {
-    let pws = get_pws(&device);
+    let mut device = device;
+    let mut pws = get_pws(&mut device);
 
     assert_lib_err!(
         LibraryError::InvalidSlot,
@@ -145,7 +148,8 @@ fn write(device: DeviceWrapper) {
 
 #[test_device]
 fn erase(device: DeviceWrapper) {
-    let pws = get_pws(&device);
+    let mut device = device;
+    let mut pws = get_pws(&mut device);
     assert_lib_err!(LibraryError::InvalidSlot, pws.erase_slot(SLOT_COUNT));
 
     assert_ok!((), pws.write_slot(0, "name", "login", "password"));
diff --git a/nitrokey/tests/util/mod.rs b/nitrokey/tests/util/mod.rs
index 49ec13e..f2b20ec 100644
--- a/nitrokey/tests/util/mod.rs
+++ b/nitrokey/tests/util/mod.rs
@@ -1,8 +1,35 @@
 // Copyright (C) 2018-2019 Robin Krahl <robin.krahl@ireas.org>
 // SPDX-License-Identifier: MIT
 
-pub static ADMIN_PASSWORD: &str = "12345678";
-pub static USER_PASSWORD: &str = "123456";
+#[macro_export]
+macro_rules! unwrap_ok {
+    ($val:expr) => {{
+        match $val {
+            Ok(val) => val,
+            Err(err) => panic!(
+                r#"assertion failed: `(left == right)`
+  left: `Ok(_)`,
+ right: `Err({:?})`"#,
+                err
+            ),
+        }
+    }};
+}
+
+#[macro_export]
+macro_rules! assert_any_ok {
+    ($val:expr) => {{
+        match &$val {
+            Ok(_) => {}
+            Err(err) => panic!(
+                r#"assertion failed: `(left == right)`
+  left: `Ok(_)`,
+ right: `Err({:?})`"#,
+                err
+            ),
+        }
+    }};
+}
 
 #[macro_export]
 macro_rules! assert_ok {