Require mutable reference if method changes device state

Previously, all methods that access a Nitrokey device took a reference
to the device as input.  This method changes methods that change the
device state to require a mutable reference instead.  In most case,
this is straightforward as the method writes data to the device (for
example write_config or change_user_pin).  But there are two edge cases:
- Authenticating with a PIN changes the device state as it may decrease
  the PIN retry counter if the authentication fails.
- Generating an HOTP code changes the device state as it increases the
  HOTP counter.

9 files changed, 163 insertions, 144 deletions

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 718b796..e98e857 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -37,6 +37,7 @@ SPDX-License-Identifier: MIT
 - 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/src/auth.rs b/src/auth.rs
index 8cec49c..f9f50fa 100644
--- a/src/auth.rs
+++ b/src/auth.rs
@@ -226,7 +226,7 @@ impl<T: Device> ops::DerefMut for User<T> {
 }
 
 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())
         })
@@ -290,7 +290,7 @@ 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);
     ///         ()
     ///     },
@@ -301,7 +301,7 @@ impl<T: Device> Admin<T> {
     /// ```
     ///
     /// [`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(
@@ -317,7 +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(
@@ -334,7 +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(
@@ -351,13 +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/src/device.rs b/src/device.rs
index 462e9dc..f6492cd 100644
--- a/src/device.rs
+++ b/src/device.rs
@@ -452,7 +452,7 @@ 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) => eprintln!("Failed to update admin PIN: {}", err),
@@ -463,7 +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 {
@@ -485,7 +485,7 @@ 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) => eprintln!("Failed to update admin PIN: {}", err),
@@ -496,7 +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 {
@@ -518,7 +518,7 @@ 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) => eprintln!("Failed to unlock user PIN: {}", err),
@@ -529,7 +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 {
@@ -552,7 +552,7 @@ 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) => eprintln!("Could not lock the Nitrokey device: {}", err),
@@ -560,7 +560,7 @@ pub trait Device: Authenticate + GetPasswordSafe + GenerateOtp + fmt::Debug {
     /// #     Ok(())
     /// # }
     /// ```
-    fn lock(&self) -> Result<(), Error> {
+    fn lock(&mut self) -> Result<(), Error> {
         get_command_result(unsafe { nitrokey_sys::NK_lock_device() })
     }
 
@@ -583,7 +583,7 @@ 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) => eprintln!("Could not perform a factory reset: {}", err),
@@ -593,7 +593,7 @@ pub trait Device: Authenticate + GetPasswordSafe + GenerateOtp + fmt::Debug {
     /// ```
     ///
     /// [`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()) })
     }
@@ -617,7 +617,7 @@ 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) => eprintln!("Could not build new AES keys: {}", err),
@@ -627,7 +627,7 @@ pub trait Device: Authenticate + GetPasswordSafe + GenerateOtp + fmt::Debug {
     /// ```
     ///
     /// [`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()) })
     }
@@ -758,8 +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> {
@@ -882,7 +882,7 @@ 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) => eprintln!("Failed to update update PIN: {}", err),
@@ -893,7 +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 {
@@ -919,7 +919,7 @@ 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) => eprintln!("Could not enter update mode: {}", err),
@@ -930,7 +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())
@@ -953,7 +953,7 @@ 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) => eprintln!("Could not enable the encrypted volume: {}", err),
@@ -964,7 +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()) })
     }
@@ -982,7 +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.");
@@ -999,7 +999,7 @@ impl Storage {
     /// #     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() })
     }
 
@@ -1028,7 +1028,7 @@ 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")?;
     /// match device.enable_hidden_volume("hidden-pw") {
     ///     Ok(()) => println!("Enabled a hidden volume."),
@@ -1041,7 +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())
@@ -1061,7 +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(()) => {
@@ -1079,7 +1079,7 @@ impl Storage {
     /// #     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() })
     }
 
@@ -1108,7 +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(())
@@ -1118,7 +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,
@@ -1148,7 +1148,7 @@ impl Storage {
     /// use nitrokey::VolumeMode;
     ///
     /// # fn try_main() -> Result<(), Error> {
-    /// let device = nitrokey::Storage::connect()?;
+    /// 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) => eprintln!("Could not set the unencrypted volume to read-write mode: {}", err),
@@ -1160,7 +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> {
@@ -1193,7 +1193,7 @@ impl Storage {
     /// use nitrokey::VolumeMode;
     ///
     /// # fn try_main() -> Result<(), Error> {
-    /// let device = nitrokey::Storage::connect()?;
+    /// 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),
@@ -1205,7 +1205,7 @@ impl Storage {
     /// [`InvalidString`]: enum.LibraryError.html#variant.InvalidString
     /// [`WrongPassword`]: enum.CommandError.html#variant.WrongPassword
     pub fn set_encrypted_volume_mode(
-        &self,
+        &mut self,
         admin_pin: &str,
         mode: VolumeMode,
     ) -> Result<(), Error> {
@@ -1322,7 +1322,7 @@ 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) => eprintln!("Could not set the clear the new SD card warning: {}", err),
@@ -1333,7 +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())
@@ -1341,7 +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() })
     }
 
@@ -1361,7 +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/src/lib.rs b/src/lib.rs
index f7da8e1..c35829c 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -47,7 +47,7 @@
 //! 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) => eprintln!("Could not write slot: {}", err),
@@ -66,7 +66,7 @@
 //! # 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) => eprintln!("Could not generate HOTP code: {}", err),
diff --git a/src/otp.rs b/src/otp.rs
index abaff66..ee142c7 100644
--- a/src/otp.rs
+++ b/src/otp.rs
@@ -38,7 +38,7 @@ 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) => eprintln!("Could not write slot: {}", err),
@@ -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).
@@ -74,7 +74,7 @@ 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) => eprintln!("Could not write slot: {}", err),
@@ -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.
     ///
@@ -106,7 +106,7 @@ 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) => eprintln!("Could not erase slot: {}", err),
@@ -119,7 +119,7 @@ pub trait ConfigureOtp {
     /// ```
     ///
     /// [`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.
     ///
@@ -136,7 +136,7 @@ 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) => eprintln!("Could not erase slot: {}", err),
@@ -149,7 +149,7 @@ pub trait ConfigureOtp {
     /// ```
     ///
     /// [`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
@@ -171,7 +171,7 @@ 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) => device.set_time(time.as_secs(), false)?,
@@ -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 {
@@ -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) => {
diff --git a/src/pws.rs b/src/pws.rs
index 1e27935..371de6e 100644
--- a/src/pws.rs
+++ b/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) => 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)?;
@@ -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,
@@ -340,8 +341,8 @@ 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) => eprintln!("Could not erase slot 0: {}", err),
@@ -351,7 +352,7 @@ impl<'a> PasswordSafe<'a> {
     /// ```
     ///
     /// [`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/tests/device.rs b/tests/device.rs
index 969a7df..7a69214 100644
--- a/tests/device.rs
+++ b/tests/device.rs
@@ -133,7 +133,7 @@ fn get_retry_count(device: DeviceWrapper) {
 
 #[test_device]
 fn config(device: DeviceWrapper) {
-    let admin = unwrap_ok!(device.authenticate_admin(ADMIN_PASSWORD));
+    let mut admin = unwrap_ok!(device.authenticate_admin(ADMIN_PASSWORD));
 
     let config = Config::new(None, None, None, true);
     assert_ok!((), admin.write_config(config));
@@ -156,6 +156,7 @@ fn change_user_pin(device: DeviceWrapper) {
     let device = device.authenticate_user(USER_PASSWORD).unwrap().device();
     let device = device.authenticate_user(USER_NEW_PASSWORD).unwrap_err().0;
 
+    let mut device = device;
     assert_ok!((), device.change_user_pin(USER_PASSWORD, USER_NEW_PASSWORD));
 
     let device = device.authenticate_user(USER_PASSWORD).unwrap_err().0;
@@ -164,6 +165,7 @@ fn change_user_pin(device: DeviceWrapper) {
         .unwrap()
         .device();
 
+    let mut device = device;
     let result = device.change_user_pin(USER_PASSWORD, USER_PASSWORD);
     assert_cmd_err!(CommandError::WrongPassword, result);
 
@@ -176,7 +178,7 @@ fn change_user_pin(device: DeviceWrapper) {
 #[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 mut device = device.authenticate_admin(ADMIN_NEW_PASSWORD).unwrap_err().0;
 
     assert_ok!(
         (),
@@ -184,7 +186,7 @@ fn change_admin_pin(device: DeviceWrapper) {
     );
 
     let device = device.authenticate_admin(ADMIN_PASSWORD).unwrap_err().0;
-    let device = device
+    let mut device = device
         .authenticate_admin(ADMIN_NEW_PASSWORD)
         .unwrap()
         .device();
@@ -220,7 +222,7 @@ where
 
 #[test_device]
 fn unlock_user_pin(device: DeviceWrapper) {
-    let device = device.authenticate_user(USER_PASSWORD).unwrap().device();
+    let mut device = device.authenticate_user(USER_PASSWORD).unwrap().device();
     assert_ok!((), device.unlock_user_pin(ADMIN_PASSWORD, USER_PASSWORD));
     assert_cmd_err!(
         CommandError::WrongPassword,
@@ -232,7 +234,7 @@ fn unlock_user_pin(device: DeviceWrapper) {
     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, USER_PASSWORD, CommandError::WrongPassword);
 
     // unblock with current PIN
     assert_cmd_err!(
@@ -246,7 +248,7 @@ fn unlock_user_pin(device: DeviceWrapper) {
     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, USER_PASSWORD, CommandError::WrongPassword);
 
     // unblock with new PIN
     assert_cmd_err!(
@@ -272,12 +274,12 @@ fn assert_utf8_err_or_ne(left: &str, right: Result<String, Error>) {
 
 #[test_device]
 fn factory_reset(device: DeviceWrapper) {
-    let admin = unwrap_ok!(device.authenticate_admin(ADMIN_PASSWORD));
+    let mut admin = unwrap_ok!(device.authenticate_admin(ADMIN_PASSWORD));
     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 = unwrap_ok!(device.get_password_safe(USER_PASSWORD));
+    let mut device = admin.device();
+    let mut pws = unwrap_ok!(device.get_password_safe(USER_PASSWORD));
     assert_ok!((), pws.write_slot(0, "test", "testlogin", "testpw"));
     drop(pws);
 
@@ -302,18 +304,20 @@ fn factory_reset(device: DeviceWrapper) {
     let user = unwrap_ok!(device.authenticate_user(USER_PASSWORD));
     assert_cmd_err!(CommandError::SlotNotProgrammed, user.get_totp_slot_name(1));
 
-    let device = user.device();
+    let mut device = user.device();
     let pws = unwrap_ok!(device.get_password_safe(USER_PASSWORD));
     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));
 }
 
 #[test_device]
 fn build_aes_key(device: DeviceWrapper) {
-    let pws = unwrap_ok!(device.get_password_safe(USER_PASSWORD));
+    let mut device = device;
+    let mut pws = unwrap_ok!(device.get_password_safe(USER_PASSWORD));
     assert_ok!((), pws.write_slot(0, "test", "testlogin", "testpw"));
     drop(pws);
 
@@ -323,7 +327,7 @@ fn build_aes_key(device: DeviceWrapper) {
     );
     assert_ok!((), device.build_aes_key(ADMIN_PASSWORD));
 
-    let device = device.authenticate_admin(ADMIN_PASSWORD).unwrap().device();
+    let mut device = device.authenticate_admin(ADMIN_PASSWORD).unwrap().device();
 
     let pws = unwrap_ok!(device.get_password_safe(USER_PASSWORD));
     assert_utf8_err_or_ne("test", pws.get_slot_name(0));
@@ -333,6 +337,7 @@ fn build_aes_key(device: DeviceWrapper) {
 
 #[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)
@@ -343,6 +348,7 @@ 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());
@@ -361,6 +367,7 @@ 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());
@@ -396,6 +403,7 @@ fn hidden_volume(device: Storage) {
 
 #[test_device]
 fn lock(device: Storage) {
+    let mut device = device;
     assert_ok!((), device.enable_encrypted_volume(USER_PASSWORD));
     assert_ok!((), device.lock());
     assert_eq!(1, count_nitrokey_block_devices());
@@ -405,6 +413,7 @@ fn lock(device: Storage) {
 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!(
         (),
@@ -441,12 +450,13 @@ fn set_unencrypted_volume_mode(device: Storage) {
         );
     }
 
-    fn assert_success(device: &Storage, mode: VolumeMode) {
+    fn assert_success(device: &mut Storage, mode: VolumeMode) {
         assert_ok!((), device.set_unencrypted_volume_mode(ADMIN_PASSWORD, 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,
@@ -454,9 +464,9 @@ fn set_unencrypted_volume_mode(device: Storage) {
     );
     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]
@@ -488,6 +498,7 @@ fn get_production_info(device: Storage) {
 
 #[test_device]
 fn clear_new_sd_card_warning(device: Storage) {
+    let mut device = device;
     assert_ok!((), device.factory_reset(ADMIN_PASSWORD));
     thread::sleep(time::Duration::from_secs(3));
     assert_ok!((), device.build_aes_key(ADMIN_PASSWORD));
@@ -506,6 +517,7 @@ fn clear_new_sd_card_warning(device: Storage) {
 
 #[test_device]
 fn export_firmware(device: Storage) {
+    let mut device = device;
     assert_cmd_err!(
         CommandError::WrongPassword,
         device.export_firmware("someadminpn")
diff --git a/tests/otp.rs b/tests/otp.rs
index fc0e79e..28a8d7c 100644
--- a/tests/otp.rs
+++ b/tests/otp.rs
@@ -4,7 +4,7 @@
 mod util;
 
 use std::fmt::Debug;
-use std::ops::Deref;
+use std::ops::DerefMut;
 
 use nitrokey::{
     Admin, Authenticate, CommandError, Config, ConfigureOtp, Device, GenerateOtp, LibraryError,
@@ -48,12 +48,12 @@ where
         .expect("Could not login as admin.")
 }
 
-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 {
             assert_ok!(code.to_string(), device.get_hotp_code(1));
@@ -63,6 +63,7 @@ fn check_hotp_codes(device: &GenerateOtp, offset: u8) {
 
 #[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));
@@ -71,36 +72,36 @@ 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 = unwrap_ok!(admin.device().authenticate_user(USER_PASSWORD));
-    check_hotp_codes(&user, 0);
+    configure_hotp(&mut admin, 0);
+    let mut user = unwrap_ok!(admin.device().authenticate_user(USER_PASSWORD));
+    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));
 
@@ -111,7 +112,7 @@ fn hotp_slot_name(device: DeviceWrapper) {
 
 #[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);
@@ -130,7 +131,7 @@ 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);
@@ -140,7 +141,7 @@ 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);
@@ -149,13 +150,13 @@ fn hotp_erase(device: DeviceWrapper) {
     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;
@@ -177,49 +178,47 @@ 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 = unwrap_ok!(admin.device().authenticate_user(USER_PASSWORD));
-    check_totp_codes(&user, 1, TotpTimestampSize::U32);
+    configure_totp(&mut admin, 1);
+    let mut user = unwrap_ok!(admin.device().authenticate_user(USER_PASSWORD));
+    check_totp_codes(&mut user, 1, TotpTimestampSize::U32);
 
     assert_cmd_err!(CommandError::NotAuthorized, user.device().get_totp_code(1));
 }
@@ -227,20 +226,20 @@ 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 = unwrap_ok!(admin.device().authenticate_user(USER_PASSWORD));
-    check_totp_codes(&user, 1, TotpTimestampSize::U64);
+    configure_totp(&mut admin, 1);
+    let mut user = unwrap_ok!(admin.device().authenticate_user(USER_PASSWORD));
+    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));
 
@@ -253,7 +252,7 @@ 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);
@@ -272,7 +271,7 @@ 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);
diff --git a/tests/pws.rs b/tests/pws.rs
index 32dc8f7..7805803 100644
--- a/tests/pws.rs
+++ b/tests/pws.rs
@@ -33,7 +33,7 @@ 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,
 {
@@ -42,6 +42,7 @@ where
 
 #[test_device]
 fn enable(device: DeviceWrapper) {
+    let mut device = device;
     assert_cmd_err!(
         CommandError::WrongPassword,
         device.get_password_safe(&(USER_PASSWORD.to_owned() + "123"))
@@ -56,8 +57,9 @@ fn enable(device: DeviceWrapper) {
 
 #[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_ok!("name".to_string(), pws.get_slot_name(1));
         let result = get_slot_name_direct(1);
@@ -72,7 +74,8 @@ 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));
     }
@@ -93,7 +96,8 @@ fn get_status(device: DeviceWrapper) {
 
 #[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_ok!("name".to_string(), pws.get_slot_name(1));
     assert_ok!("login".to_string(), pws.get_slot_login(1));
@@ -119,7 +123,8 @@ 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,
@@ -144,7 +149,8 @@ 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"));