test(core): add video buffer and palette tests

tests/Chip8.Tests/PaletteTests.cs

@@ -0,0 +1,91 @@
+using System;
+using Chip8.Core;
+using Xunit;
+
+namespace Chip8.Tests;
+
+public class PaletteTests
+{
+    [Fact]
+    public void hexParsesWithAndWithoutHash()
+    {
+        var withHash = Rgb.fromHex("#1A2B3C");
+        var without = Rgb.fromHex("1A2B3C");
+        Assert.Equal(withHash, without);
+        Assert.Equal(0x1A, withHash.r);
+        Assert.Equal(0x2B, withHash.g);
+        Assert.Equal(0x3C, withHash.b);
+    }
+
+    [Fact]
+    public void hexRoundTripsThroughToHex()
+    {
+        var color = new Rgb(0xFF, 0x80, 0x00);
+        Assert.Equal("#FF8000", color.toHex());
+        Assert.Equal(color, Rgb.fromHex(color.toHex()));
+    }
+
+    [Theory]
+    [InlineData("12345")]
+    [InlineData("#12")]
+    [InlineData("XYZXYZ")]
+    public void malformedHexThrows(string value)
+    {
+        Assert.Throws<FormatException>(() => Rgb.fromHex(value));
+    }
+
+    [Fact]
+    public void monochromePaletteHasTwoColors()
+    {
+        var palette = Palette.monochrome();
+        Assert.Equal(2, palette.colorCount);
+        Assert.Equal(new Rgb(0, 0, 0), palette[0]);
+        Assert.Equal(new Rgb(0xFF, 0xFF, 0xFF), palette[1]);
+    }
+
+    [Fact]
+    public void octoPaletteHasFourColors()
+    {
+        var palette = Palette.octo();
+        Assert.Equal(4, palette.colorCount);
+        Assert.Equal(Rgb.fromHex("#996600"), palette[0]);
+        Assert.Equal(Rgb.fromHex("#662200"), palette[3]);
+    }
+
+    [Fact]
+    public void extendedPaletteHasSixteenColors()
+    {
+        Assert.Equal(16, Palette.extended16().colorCount);
+    }
+
+    [Fact]
+    public void resolveWrapsIndexIntoRange()
+    {
+        var palette = Palette.grayscale();
+        Assert.Equal(palette[0], palette.resolve(4));
+        Assert.Equal(palette[1], palette.resolve(5));
+        Assert.Equal(palette[0], palette.resolve(-1));
+    }
+
+    [Theory]
+    [InlineData("mono")]
+    [InlineData("grayscale")]
+    [InlineData("octo")]
+    [InlineData("extended16")]
+    public void byNameResolvesKnownPalettes(string name)
+    {
+        Assert.True(Palette.byName(name).colorCount >= 2);
+    }
+
+    [Fact]
+    public void byNameRejectsUnknownPalette()
+    {
+        Assert.Throws<ArgumentException>(() => Palette.byName("neon"));
+    }
+
+    [Fact]
+    public void paletteRejectsSingleColor()
+    {
+        Assert.Throws<ArgumentException>(() => new Palette(new Rgb(0, 0, 0)));
+    }
+}