test: write tests for facebook provider login

Author: russellwheatley

packages/firebase_ui_oauth_facebook/lib/src/provider.dart

@@ -36,6 +36,7 @@ class FacebookProvider extends OAuthProvider {
   });
 
   /// Generates a cryptographically secure random nonce for limited login
+  @visibleForTesting
   String _generateNonce([int length = 32]) {
     const charset =
         '0123456789ABCDEFGHIJKLMNOPQRSTUVXYZabcdefghijklmnopqrstuvwxyz-._';
@@ -45,13 +46,15 @@ class FacebookProvider extends OAuthProvider {
   }
 
   /// Returns the SHA256 hash of the given string
+  @visibleForTesting
   String _sha256ofString(String input) {
     final bytes = utf8.encode(input);
     final digest = sha256.convert(bytes);
     return digest.toString();
   }
 
   /// Checks if tracking permission has been granted on iOS
+  @visibleForTesting
   Future<bool> _hasTrackingPermission() async {
     // Only check on iOS
     if (defaultTargetPlatform != TargetPlatform.iOS) {
@@ -67,6 +70,7 @@ class FacebookProvider extends OAuthProvider {
     }
   }
 
+  @visibleForTesting
   void _handleResult(LoginResult result, AuthAction action) {
     switch (result.status) {
       case LoginStatus.success:
@@ -174,3 +178,26 @@ class FacebookProvider extends OAuthProvider {
     return true;
   }
 }
+
+// Extension to expose private methods and fields for testing
+extension FacebookProviderTestExtension on FacebookProvider {
+  String generateNonceForTest([int length = 32]) {
+    return _generateNonce(length);
+  }
+
+  String sha256ForTest(String input) {
+    return _sha256ofString(input);
+  }
+
+  Future<bool> hasTrackingPermissionForTest() {
+    return _hasTrackingPermission();
+  }
+
+  void handleResultForTest(LoginResult result, AuthAction action) {
+    _handleResult(result, action);
+  }
+
+  void setRawNonceForTest(String? nonce) {
+    _rawNonce = nonce;
+  }
+}

packages/firebase_ui_oauth_facebook/pubspec.yaml

@@ -20,6 +20,8 @@ dev_dependencies:
   flutter_test:
     sdk: flutter
   flutter_lints: ^3.0.1
+  mockito: ^5.4.4
+  build_runner: ^2.4.13
 
 # For information on the generic Dart part of this file, see the
 # following page: https://dart.dev/tools/pub/pubspec