Add some unit tests for KeySpline

tests/Avalonia.Animation.UnitTests/KeySplineTests.cs

@@ -0,0 +1,48 @@
+using System;
+using Avalonia.Controls;
+using Avalonia.UnitTests;
+using Xunit;
+
+namespace Avalonia.Animation.UnitTests
+{
+    public class KeySplineTests
+    {
+        [Theory]
+        [InlineData("1,2 3,4")]
+        [InlineData("1 2 3 4")]
+        [InlineData("1 2,3 4")]
+        [InlineData("1,2,3,4")]
+        public void Can_Parse_KeySpline_Via_TypeConverter(string input)
+        {
+            var conv = new KeySplineTypeConverter();
+
+            var keySpline = (KeySpline)conv.ConvertFrom(input);
+
+            Assert.Equal(1, keySpline.ControlPointX1);
+            Assert.Equal(2, keySpline.ControlPointY1);
+            Assert.Equal(3, keySpline.ControlPointX2);
+            Assert.Equal(4, keySpline.ControlPointY2);
+        }
+
+        [Theory]
+        [InlineData(0.00)]
+        [InlineData(0.50)]
+        [InlineData(1.00)]
+        public void KeySpline_X_Values_In_Range_Do_Not_Throw(double input)
+        {
+            var keySpline = new KeySpline();
+            keySpline.ControlPointX1 = input; // no exception will be thrown -- test will fail if exception thrown
+            keySpline.ControlPointX2 = input; // no exception will be thrown -- test will fail if exception thrown
+        }
+
+        [Theory]
+        [InlineData(-0.01)]
+        [InlineData(1.01)]
+        public void KeySpline_X_Values_Cannot_Be_Out_Of_Range(double input)
+        {
+            var keySpline = new KeySpline();
+            Assert.Throws<ArgumentException>(() => keySpline.ControlPointX1 = input);
+            Assert.Throws<ArgumentException>(() => keySpline.ControlPointX2 = input);
+        }
+    }
+}