Update ColorNumericsTests.cs

tests/ImageSharp.Tests/Helpers/ColorNumericsTests.cs

@@ -24,5 +24,59 @@ public class ColorNumericsTests
         Assert.Equal(expected, actual);
     }
 
-    // TODO: We need to test all ColorNumerics methods!
+    [Theory]
+    [InlineData((ushort)0, (byte)0)]
+    [InlineData((ushort)128, (byte)0)]
+    [InlineData((ushort)129, (byte)1)]
+    [InlineData((ushort)257, (byte)1)]
+    [InlineData((ushort)32896, (byte)128)]
+    [InlineData(ushort.MaxValue, byte.MaxValue)]
+    public void From16BitTo8Bit_ReturnsExpectedValue(ushort component, byte expected)
+    {
+        byte actual = ColorNumerics.From16BitTo8Bit(component);
+
+        Assert.Equal(expected, actual);
+    }
+
+    [Fact]
+    public void From16BitTo8Bit_RoundTripsAllExpanded8BitValues()
+    {
+        for (int i = 0; i <= byte.MaxValue; i++)
+        {
+            byte expected = (byte)i;
+            ushort component = ColorNumerics.From8BitTo16Bit(expected);
+
+            byte actual = ColorNumerics.From16BitTo8Bit(component);
+
+            Assert.Equal(expected, actual);
+        }
+    }
+
+    [Theory]
+    [InlineData(0U, (byte)0)]
+    [InlineData(8421504U, (byte)0)]
+    [InlineData(8421505U, (byte)1)]
+    [InlineData(16843009U, (byte)1)]
+    [InlineData(2155905152U, (byte)128)]
+    [InlineData(uint.MaxValue, byte.MaxValue)]
+    public void From32BitTo8Bit_ReturnsExpectedValue(uint component, byte expected)
+    {
+        byte actual = ColorNumerics.From32BitTo8Bit(component);
+
+        Assert.Equal(expected, actual);
+    }
+
+    [Fact]
+    public void From32BitTo8Bit_RoundTripsAllExpanded8BitValues()
+    {
+        for (int i = 0; i <= byte.MaxValue; i++)
+        {
+            byte expected = (byte)i;
+            uint component = ColorNumerics.From8BitTo32Bit(expected);
+
+            byte actual = ColorNumerics.From32BitTo8Bit(component);
+
+            Assert.Equal(expected, actual);
+        }
+    }
 }