test(otp): Add unit tests for IsValidSequenceProgression method

Author: DennisDyallo

Yubico.YubiKey/src/Yubico/YubiKey/Pipelines/OtpErrorTransform.cs

@@ -60,7 +60,7 @@ public ResponseApdu Invoke(CommandApdu command, Type commandType, Type responseT
                 var responseApdu = _nextTransform.Invoke(command, commandType, responseType);
                 var readStatusResponse = new ReadStatusResponse(responseApdu);
                 var otpStatus = readStatusResponse.GetData();
-                byte nextSequence = otpStatus.SequenceNumber;
+                int nextSequence = otpStatus.SequenceNumber;
 
                 // If we see the sequence number change, we can assume that the configuration was applied successfully. Otherwise
                 // we just invent an error in the response.
@@ -82,7 +82,7 @@ public ResponseApdu Invoke(CommandApdu command, Type commandType, Type responseT
 
         public void Cleanup() => _nextTransform.Cleanup();
 
-        private static bool IsValidSequenceProgression(int beforeSequence, int nextSequence, OtpStatus afterStatus)
+        internal static bool IsValidSequenceProgression(int beforeSequence, int nextSequence, OtpStatus afterStatus)
         {
             const int configStatusMask = 0x1F;
 

Yubico.YubiKey/tests/unit/Yubico/YubiKey/Pipelines/OtpErrorTransformTests.cs

@@ -0,0 +1,74 @@
+using Xunit;
+using Yubico.YubiKey.Otp;
+
+namespace Yubico.YubiKey.Pipelines;
+
+public class OtpErrorTransformTests
+{
+    [Theory]
+    [InlineData(0, 1)]      // First increment
+    [InlineData(5, 6)]      // Normal increment  
+    [InlineData(254, 255)]  // Near byte boundary
+    [InlineData(257, 258)]  // Near byte boundary
+    
+    public void IsValidSequenceProgression_NormalIncrement_ReturnsTrue(int before, int after)
+    {
+        var status = CreateOtpStatus(touchLevel: 0xFF); // TouchLevel irrelevant
+        
+        bool isValid = OtpErrorTransform.IsValidSequenceProgression(before, after, status);
+        
+        Assert.True(isValid);
+    }
+
+    [Theory]
+    [InlineData(0, 2)]      // Skip increment
+    [InlineData(5, 7)]      // Jump by 2
+    [InlineData(10, 8)]     // Backwards
+    public void IsValidSequenceProgression_InvalidIncrement_ReturnsFalse(int before, int after)
+    {
+        var status = CreateOtpStatus(touchLevel: 0x00); // TouchLevel irrelevant
+        
+        bool isValid = OtpErrorTransform.IsValidSequenceProgression(before, after, status);
+        
+        Assert.False(isValid);
+    }
+
+    [Theory]
+    [InlineData(1, 0x00)]   // Config bits clear
+    [InlineData(5, 0x20)]   // Upper bits set, config clear  
+    [InlineData(255, 0xE0)] // Multiple upper bits, config clear
+    public void IsValidSequenceProgression_ValidReset_ReturnsTrue(int before, byte touchLevel)
+    {
+        var status = CreateOtpStatus(touchLevel);
+        
+        bool isValid = OtpErrorTransform.IsValidSequenceProgression(before, 0, status);
+        
+        Assert.True(isValid);
+    }
+
+    [Theory]
+    [InlineData(0, 0x00)]   // Already zero (invalid before state)
+    [InlineData(1, 0x01)]   // Config bit set
+    [InlineData(5, 0x1F)]   // All config bits set
+    [InlineData(5, 0x21)]   // Config + upper bits set
+    public void IsValidSequenceProgression_InvalidReset_ReturnsFalse(int before, byte touchLevel)
+    {
+        var status = CreateOtpStatus(touchLevel);
+        
+        bool isValid = OtpErrorTransform.IsValidSequenceProgression(before, 0, status);
+        
+        Assert.False(isValid);
+    }
+
+    private static OtpStatus CreateOtpStatus(byte touchLevel) => new()
+    {
+        FirmwareVersion = new FirmwareVersion(),
+        SequenceNumber = 0,
+        TouchLevel = touchLevel,
+        ShortPressConfigured = false,
+        LongPressConfigured = false,
+        ShortPressRequiresTouch = false,
+        LongPressRequiresTouch = false,
+        LedBehaviorInverted = false
+    };
+}