Count the whole conversation against the model's window

app/Tests/Chat/TokenAmountTests.cs

@@ -0,0 +1,54 @@
+using System.Globalization;
+
+using AIStudio.Chat;
+
+namespace AIStudio.Tests.Chat;
+
+/// <summary>
+/// Checks how a number of tokens is written under the input field.
+/// </summary>
+/// <remarks>
+/// The culture is an argument rather than something taken from the machine, and that is the point
+/// being checked as much as the digits are: AI Studio's language is chosen in its own settings, so
+/// the thread's culture says nothing about which separators a person expects to read.
+/// </remarks>
+[TestFixture]
+public sealed class TokenAmountTests
+{
+    private static readonly CultureInfo AMERICAN = CultureInfo.GetCultureInfo("en-US");
+
+    private static readonly CultureInfo GERMAN = CultureInfo.GetCultureInfo("de-DE");
+
+    [TestCase(0, "0")]
+    [TestCase(7, "7")]
+    [TestCase(847, "847")]
+    [TestCase(999, "999", Description = "The last number written out in full.")]
+    [TestCase(1_000, "1.00k")]
+    [TestCase(1_234, "1.23k")]
+    [TestCase(12_347, "12.35k")]
+    [TestCase(128_000, "128.00k")]
+    [TestCase(400_000, "400.00k")]
+    [TestCase(999_499, "999.50k")]
+    [TestCase(999_999, "1.00M", Description = "Rounded before the unit is chosen, so it does not read as 1,000.00k.")]
+    [TestCase(1_000_000, "1.00M")]
+    [TestCase(1_048_576, "1.05M")]
+    [TestCase(1_050_000, "1.05M", Description = "Which is how OpenAI writes it themselves.")]
+    [TestCase(2_000_000, "2.00M")]
+    public void ANumberOfTokensIsWrittenTheWayItIsRead(int tokens, string wanted)
+    {
+        Assert.That(TokenAmount.Format(tokens, AMERICAN), Is.EqualTo(wanted));
+    }
+
+    [TestCase(999, "999")]
+    [TestCase(1_234, "1,23k")]
+    [TestCase(400_000, "400,00k")]
+    [TestCase(1_048_576, "1,05M")]
+    public void TheSeparatorsAreTheOnesTheUserKnows(int tokens, string wanted)
+    {
+        //
+        // A German reads 1,23k where an American reads 1.23k. Writing either of them the other way
+        // around reads as a number a thousand times off.
+        //
+        Assert.That(TokenAmount.Format(tokens, GERMAN), Is.EqualTo(wanted));
+    }
+}