Added tests for the configurable transcription Opus bitrate

app/Tests/Settings/TranscriptionOpusBitrateTests.cs

@@ -0,0 +1,54 @@
+using AIStudio.Settings.DataModel;
+
+namespace AIStudio.Tests.Settings;
+
+/// <summary>
+/// Checks which bitrate the transcription pipeline ends up asking the Opus encoder for.
+/// </summary>
+/// <remarks>
+/// This number is the whole reason the setting exists. Until v26.9.1 the encoder was fixed at
+/// 32 kbps, and transcription models silently dropped what had been spoken quietly -- a greeting at
+/// the start of a recording never reached the transcript. Two ways back to that value have to stay
+/// closed: the arm catching a bitrate nobody declared, and the member a settings file the app cannot
+/// read falls back to. Both are one edit away from pointing at the lowest quality again.
+/// </remarks>
+[TestFixture]
+public sealed class TranscriptionOpusBitrateTests
+{
+    private static readonly Dictionary<TranscriptionOpusBitrate, uint> EXPECTED_BITS_PER_SECOND = new()
+    {
+        [TranscriptionOpusBitrate.KBPS_32] = 32_000,
+        [TranscriptionOpusBitrate.KBPS_64] = 64_000,
+        [TranscriptionOpusBitrate.KBPS_128] = 128_000,
+        [TranscriptionOpusBitrate.KBPS_256] = 256_000,
+    };
+
+    [Test]
+    public void EveryOfferedBitrateAsksForWhatItsNameSays()
+    {
+        foreach (var bitrate in Enum.GetValues<TranscriptionOpusBitrate>())
+        {
+            Assert.That(EXPECTED_BITS_PER_SECOND.ContainsKey(bitrate), Is.True, $"The selection offers {bitrate}, so this test has to state what that is worth in bits per second.");
+            Assert.That(bitrate.GetBitsPerSecond(), Is.EqualTo(EXPECTED_BITS_PER_SECOND[bitrate]), $"{bitrate} is what the user picked; anything else travels to the encoder behind their back.");
+        }
+    }
+
+    [Test]
+    public void ABitrateNobodyDeclaredFallsBackToTheRecommendedOne()
+    {
+        var undeclared = (TranscriptionOpusBitrate)999;
+
+        Assert.That(Enum.IsDefined(undeclared), Is.False, "The point of this test is a value outside the enum; a declared one would prove nothing.");
+        Assert.That(undeclared.GetBitsPerSecond(), Is.EqualTo(128_000u), "Not knowing which quality was meant is no reason to pick the worst one available.");
+    }
+
+    [Test]
+    public void AnUnreadableSettingsValueLandsOnTheRecommendedBitrate()
+    {
+        //
+        // TolerantEnumConverter answers a value it cannot parse with the member whose underlying
+        // value is zero. Which member that is decides what a damaged settings file transcribes with:
+        //
+        Assert.That(default(TranscriptionOpusBitrate), Is.EqualTo(TranscriptionOpusBitrate.KBPS_128), "The member with the underlying value zero is what a settings file the app cannot read falls back to, so it has to be the recommended bitrate.");
+    }
+}