Fix BezierAnimation fraction issue (#463)

Author: Kyle-Ye

Example/HostingExample/ViewController.swift

@@ -66,6 +66,6 @@ class ViewController: NSViewController {
 
 struct ContentView: View {
     var body: some View {
-        ColorViewControllerRepresentableExample()
+        ColorAnimationExample()
     }
 }

Example/SharedExample/Animation/ColorAnimationExample.swift

@@ -15,9 +15,9 @@ struct ColorAnimationExample: View {
             Color(platformColor: showRed ? .red : .blue)
                 .frame(width: showRed ? 200 : 400, height: showRed ? 200 : 400)
         }
-        .animation(.easeInOut(duration: 2), value: showRed)
+        .animation(.easeInOut(duration: 5), value: showRed)
         .onAppear {
-            DispatchQueue.main.asyncAfter(deadline: .now() + 2) {
+            DispatchQueue.main.asyncAfter(deadline: .now() + 1) {
                 showRed.toggle()
             }
         }

Sources/OpenSwiftUICore/Animation/Animatable/AnimatablePair.swift

@@ -76,6 +76,6 @@ extension AnimatablePair: Sendable where First: Sendable, Second: Sendable {}
 
 extension AnimatablePair: CustomDebugStringConvertible {
     public var debugDescription: String {
-        "\(first), \(second)"
+        "(\(first), \(second))"
     }
 }

Sources/OpenSwiftUICore/Animation/Animation/BezierAnimation.swift

@@ -489,7 +489,7 @@ package struct BezierAnimation: InternalCustomAnimation {
         guard duration > 0, duration >= elapsed else {
             return nil
         }
-        return curve.value(at: elapsed.clamp(min: 0.0, max: 1.0))
+        return curve.value(at: (elapsed / duration).clamp(min: 0.0, max: 1.0))
     }
 
     package var function: Animation.Function {

Tests/OpenSwiftUICoreTests/Animation/Animation/BezierAnimationTests.swift

@@ -0,0 +1,32 @@
+//
+//  BezierAnimationTests.swift
+//  OpenSwiftUICoreTests
+
+import OpenSwiftUICore
+import Testing
+import Numerics
+
+// MARK: - BezierAnimationTests
+
+struct BezierAnimationTests {
+    @Test(
+        .bug(
+            "https://github.com/OpenSwiftUIProject/OpenSwiftUI/issues/459",
+            id: "459",
+            "BezierAnimation's fraction is behavior like a fixed 1 time duration animation"
+        )
+    )
+    func fraction() throws {
+        let animation = BezierAnimation(
+            curve: .init(
+                startControlPoint: .topLeading,
+                endControlPoint: .bottomTrailing
+            ),
+            duration: 100
+        )
+        let f1 = try #require(animation.fraction(for: 10.0))
+        let f2 = try #require(animation.fraction(for: 50.0))
+        #expect(f1.isApproximatelyEqual(to: 0.1, absoluteTolerance: 0.01))
+        #expect(f2.isApproximatelyEqual(to: 0.5, absoluteTolerance: 0.01))
+    }
+}