Add unit tests

Author: ccwork288

Package.swift

@@ -15,5 +15,6 @@ let package = Package(
         .target(
             name: "SplitView",
             dependencies: []),
+        .testTarget(name: "SplitViewTests", dependencies: ["SplitView"]),
     ]
 )

Tests/SplitViewTests/SplitViewTests.swift

@@ -1,11 +1,67 @@
 import XCTest
+import SwiftUI
 @testable import SplitView
 
+struct ContentView: View {
+    let hide = SideHolder()
+    var body: some View {
+        VStack(spacing: 0) {
+            Button("Toggle Hide") {
+                withAnimation {
+                    hide.toggle()   // Toggle between hiding nothing and hiding secondary
+                }
+            }
+            HSplit(left: { Color.red }, right: { Color.green })
+                .hide(hide)
+                .constraints(minPFraction: 0.2, minSFraction: 0.2)
+                .splitter { Splitter.invisible() }
+        }
+    }
+}
+
 final class SplitViewTests: XCTestCase {
-    func testExample() throws {
-        // This is an example of a functional test case.
-        // Use XCTAssert and related functions to verify your tests produce the correct
-        // results.
-        XCTAssertEqual(SplitView().text, "Hello, World!")
+    func testSplitViewHideSecondary() {
+        let view = ContentView()
+        let hide = view.hide
+        
+        // Initial state: Both primary (red) and secondary (green) views are visible.
+        XCTAssertNil(hide.side)
+        
+        // Toggle hide to hide the secondary (green) view.
+        withAnimation {
+            hide.toggle()
+        }
+        XCTAssertEqual(hide.side, .secondary)
+        
+        // Toggle hide again to unhide the secondary (green) view.
+        withAnimation {
+            hide.toggle()
+        }
+        XCTAssertNil(hide.side)
+    }
+    
+    func testSplitViewHidPrimary() {
+        let view = ContentView()
+        let hide = view.hide
+        
+        // Initial state: Both primary (red) and secondary (green) views are visible.
+        XCTAssertNil(hide.side)
+
+        // Set the previous value to .primary (to simulate the initial old value)
+        hide.side = .primary
+        XCTAssertEqual(hide.side, .primary)
+
+        // Toggle to unhide the primary side (red view).
+        hide.toggle()
+        XCTAssertNil(hide.side)
+
+        // Toggle to hide the primary side again (red view).
+        hide.toggle()
+        XCTAssertEqual(hide.side, .primary)
+
+        // Toggle to unhide the primary side again (red view).
+        hide.toggle()
+        XCTAssertNil(hide.side)
     }
 }
+