fix: Test initial app link by mocking the event channel

Author: bruiken

packages/supabase_flutter/test/supabase_flutter_test.dart

@@ -1,3 +1,4 @@
+import 'package:flutter/services.dart';
 import 'package:flutter_test/flutter_test.dart';
 import 'package:supabase_flutter/supabase_flutter.dart';
 
@@ -93,11 +94,12 @@ void main() {
 
   group('Deep Link with PKCE code', () {
     late final PkceHttpClient pkceHttpClient;
+    late final EventChannel appLinksEventChannel;
     setUp(() async {
       pkceHttpClient = PkceHttpClient();
 
       // Add initial deep link with a `code` parameter
-      mockAppLink(
+      appLinksEventChannel = mockAppLink(
         initialLink: 'com.supabase://callback/?code=my-code-verifier',
       );
       await Supabase.initialize(
@@ -118,6 +120,9 @@ void main() {
     test(
         'Having `code` as the query parameter triggers `getSessionFromUrl` call on initialize',
         () async {
+      // Wait for the initial app link to be handled, as this is an async process
+      final stream = appLinksEventChannel.receiveBroadcastStream();
+      await stream.first;
       expect(pkceHttpClient.requestCount, 1);
       expect(pkceHttpClient.lastRequestBody['auth_code'], 'my-code-verifier');
     });

packages/supabase_flutter/test/widget_test_stubs.dart

@@ -94,10 +94,12 @@ class MockEmptyLocalStorage extends LocalStorage {
   Future<void> removePersistedSession() async {}
 }
 
-/// Registers the mock handler for uni_links
-void mockAppLink({String? initialLink}) {
+/// Registers the mock handler for app_links
+///
+/// Returns the [EventChannel] used to mock the incoming links.
+EventChannel mockAppLink({String? initialLink}) {
   const channel = MethodChannel('com.llfbandit.app_links/messages');
-  const anotherChannel = MethodChannel('com.llfbandit.app_links/events');
+  const eventChannel = EventChannel('com.llfbandit.app_links/events');
 
   TestWidgetsFlutterBinding.ensureInitialized();
 
@@ -107,7 +109,16 @@ void mockAppLink({String? initialLink}) {
 
   // ignore: invalid_null_aware_operator
   TestDefaultBinaryMessengerBinding.instance?.defaultBinaryMessenger
-      .setMockMethodCallHandler(anotherChannel, (message) async => null);
+      .setMockStreamHandler(
+    eventChannel,
+    MockStreamHandler.inline(
+      onListen: (arguments, events) {
+        events.success(initialLink);
+      },
+    ),
+  );
+
+  return eventChannel;
 }
 
 class MockAsyncStorage extends GotrueAsyncStorage {