Add spring unit tests

tests/Avalonia.Base.UnitTests/Animation/SpringTests.cs

@@ -0,0 +1,118 @@
+using System;
+using Avalonia.Animation;
+using Avalonia.Animation.Easings;
+using Avalonia.Controls.Shapes;
+using Avalonia.Media;
+using Avalonia.Styling;
+using Xunit;
+
+namespace Avalonia.Base.UnitTests.Animation;
+
+public class SpringTests
+{
+    [Theory]
+    [InlineData("1,2 3,4")]
+    public void Can_Parse_Spring_Via_TypeConverter(string input)
+    {
+        var conv = new SpringTypeConverter();
+
+        var spring = (Spring)conv.ConvertFrom(input);
+
+        Assert.Equal(1, spring.Mass);
+        Assert.Equal(2, spring.Stiffness);
+        Assert.Equal(3, spring.Damping);
+        Assert.Equal(4, spring.InitialVelocity);
+    }
+
+    [Theory]
+    [InlineData("1,2F,3,4")] 
+    [InlineData("Foo,Bar,Fee,Buzz")] 
+    public void Can_Handle_Invalid_String_Via_TypeConverter(string input)
+    {
+        var conv = new SpringTypeConverter();
+
+        Assert.ThrowsAny<Exception>(() => (Spring)conv.ConvertFrom(input));
+    }
+
+    [Fact]
+    public void SplineEasing_Can_Be_Mutated()
+    {
+        var easing = new SpringEasing(1, 1, 1, 0);
+
+        Assert.Equal(0, easing.Ease(0));
+        Assert.Equal(0.34029984660829826, easing.Ease(1));
+
+        easing.Mass = 2;
+        easing.Stiffness = 2;
+        easing.Damping = 2;
+        easing.InitialVelocity = 1;
+
+        Assert.NotEqual(0.05136985716812037, easing.Ease(0.5));
+    }
+
+    [Fact]
+    public void Check_SpringEasing_Handled_properly()
+    {
+        var keyframe1 = new KeyFrame()
+        {
+            Setters =
+            {
+                new Setter(RotateTransform.AngleProperty, -2.5d),
+            },
+            KeyTime = TimeSpan.FromSeconds(0)
+        };
+
+        var keyframe2 = new KeyFrame()
+        {
+            Setters =
+            {
+                new Setter(RotateTransform.AngleProperty, 2.5d),
+            },
+            KeyTime = TimeSpan.FromSeconds(5)
+        };
+
+        var animation = new Avalonia.Animation.Animation()
+        {
+            Duration = TimeSpan.FromSeconds(5),
+            Children =
+            {
+                keyframe1,
+                keyframe2
+            },
+            IterationCount = new IterationCount(5),
+            PlaybackDirection = PlaybackDirection.Alternate,
+            Easing = new SpringEasing(1, 10, 1, 0)
+        };
+
+        var rotateTransform = new RotateTransform(-2.5);
+        var rect = new Rectangle()
+        {
+            RenderTransform = rotateTransform
+        };
+
+        var clock = new TestClock();
+        var animationRun = animation.RunAsync(rect, clock);
+
+        clock.Step(TimeSpan.Zero);
+        Assert.Equal(rotateTransform.Angle, -2.5);
+        clock.Step(TimeSpan.FromSeconds(5));
+        Assert.Equal(rotateTransform.Angle, 5.522828945000075);
+
+        var tolerance = 0.01;
+        clock.Step(TimeSpan.Parse("00:00:10.0153932"));
+        var expected = -2.499763294237805;
+        Assert.True(Math.Abs(rotateTransform.Angle - expected) <= tolerance);
+
+        clock.Step(TimeSpan.Parse("00:00:11.2655407"));
+        expected = -1.1011448950348934;
+        Assert.True(Math.Abs(rotateTransform.Angle - expected) <= tolerance);
+
+        clock.Step(TimeSpan.Parse("00:00:12.6158773"));
+        expected = 2.1264981706749007;
+        Assert.True(Math.Abs(rotateTransform.Angle - expected) <= tolerance);
+
+        clock.Step(TimeSpan.Parse("00:00:14.6495256"));
+        expected = 5.4337608446234782;
+        Assert.True(Math.Abs(rotateTransform.Angle - expected) <= tolerance);
+    }
+}