[webview_flutter_wkwebview] Fixes crash when running WKNavigationResponse tests on Xcode 26 (#10316)

Fixes flutter/flutter#173326

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Author: bparrishMines

packages/webview_flutter/webview_flutter_wkwebview/darwin/Tests/NavigationDelegateProxyAPITests.swift

@@ -62,7 +62,7 @@ class NavigationDelegateProxyAPITests: XCTestCase {
     let registrar = TestProxyApiRegistrar()
     let instance = NavigationDelegateImpl(api: api, registrar: registrar)
     let webView = WKWebView(frame: .zero)
-    let navigationResponse = TestNavigationResponse()
+    let navigationResponse = TestNavigationResponse.instance
 
     var result: WKNavigationResponsePolicy?
     let callbackExpectation = expectation(description: "Wait for callback.")

packages/webview_flutter/webview_flutter_wkwebview/darwin/Tests/NavigationResponseProxyAPITests.swift

@@ -12,7 +12,7 @@ class NavigationResponseProxyAPITests: XCTestCase {
     let registrar = TestProxyApiRegistrar()
     let api = registrar.apiDelegate.pigeonApiWKNavigationResponse(registrar)
 
-    let instance = WKNavigationResponse()
+    let instance = TestNavigationResponse.instance
     let value = try? api.pigeonDelegate.response(pigeonApi: api, pigeonInstance: instance)
 
     XCTAssertEqual(value, instance.response)
@@ -22,16 +22,24 @@ class NavigationResponseProxyAPITests: XCTestCase {
     let registrar = TestProxyApiRegistrar()
     let api = registrar.apiDelegate.pigeonApiWKNavigationResponse(registrar)
 
-    let instance = TestNavigationResponse()
+    let instance = TestNavigationResponse.instance
     let value = try? api.pigeonDelegate.isForMainFrame(pigeonApi: api, pigeonInstance: instance)
 
     XCTAssertEqual(value, instance.isForMainFrame)
   }
 }
 
 class TestNavigationResponse: WKNavigationResponse {
+  // Provides a static instance to prevent a crash when a WKNavigationResponse is deallocated
+  // See https://github.com/flutter/flutter/issues/173326
+  static let instance = TestNavigationResponse()
+
   let testResponse = URLResponse()
 
+  private override init() {
+    super.init()
+  }
+
   override var isForMainFrame: Bool {
     return true
   }