Flutter mocking a ChangeNotifierProvider and setting provider values

Question

Ok, bear with me as I am just beginning to learn widget testing. I have a MainAppBar widget that has an AuthProvider above it in the widget tree, which is necessary to do an auth check and subsequent logout if a user is in fact authenticated. This is a silly scenario, but being able to test it will be useful for many other scenarios in my app.

IconButton(
 icon: Icon(Icons.logout), 
 onPressed: () {
   if (Provider.of<AuthProvider>(context, listen: false).isAuthenticated) {
     Provider.of<AuthProvider>(context, listen: false).signOut();
     Navigator.pushReplacementNamed(context, '/login');
   }
 }
)

I am mocking the AuthProvider like so

class MockAuthProvider extends Mock implements AuthProvider {}

with mockito and wrapping the widget like so

MockAuthProvider mockAuthProvider = MockAuthProvider();
  
Widget makeTestableWidget({Widget child}) => MaterialApp(
  home: ChangeNotifierProvider<AuthProvider>(
    create: (_) => mockAuthProvider,
    child: Scaffold(
      body: child,
    ),
  ),
);

The isAuthenticated bool is based on a simple enum status check, so as long as I set the status, I can test for true and false scenarios, etc. In my test I would like to set a status and test whether signOut and Navigator are called or not.

testWidgets('Clicking on logout icon...', (WidgetTester tester) async {
  mockAuthProvider.setAuthProviderStatus(AuthProviderStatus.Unauthenticated);
  print(mockAuthProvider.isAuthenticated);
  await tester.pumpWidget(makeTestableWidget(child: MainAppBar(title: 'test')));
    
  var icon = find.byIcon(Icons.logout);
  await tester.tap(icon);
  await tester.pump();

  verifyNever(mockAuthProvider.signOut());
});

The setAuthProviderStatus setter sets the status and the isAuthenticated does a basic check:

bool get isAuthenticated {
  if (status == AuthProviderStatus.Authenticated) {
    return true;
  }
  return false;
}

The AuthProvider initializes the status as a default of Uninitialized, so though this check could be expanded to consider null, it should be fine for now. In my MainAppBar widget, the isAuthenticated bool is coming back as null and throwing the exception Failed assertion: boolean expression must not be null since the if statement requires a bool and null causes it to fail. The print in my test print(mockAuthProvider.isAuthenticated); is also null. I've successfully tested with passing the actual AuthProvider and am not having the same issue, though that clearly will not work for testing purposes.

How can I set values in a mock Provider so that the widgets that are under them are are aware of them?

Answer 1

In case someone stumbles on this... To achieve this, you can stub any provider functionality as needed:

Instead of:

mockAuthProvider.setAuthProviderStatus(AuthProviderStatus.Unauthenticated);  

you can use mockito like so:

when(mockAuthProvider.isAuthenticated)
  .thenReturn(<VALUE YOU WANT TO TEST>);

so when the line Provider.of<AuthProvider>(context, listen: false).isAuthenticated is executed, isAuthenticated will have a stubbed value.

Here are the tests I ended up writing for that Icon's onPressed functionality:

void setIsAuthenticated(bool isAuthenticated) {
  when(mockAuthProvider.isAuthenticated)
    .thenReturn(isAuthenticated);
  when(mockAuthProvider.hasListeners).thenReturn(false);
}

testWidgets('Clicking on logout icon does not call signOut if user is not authenticated', (WidgetTester tester) async {
  setIsAuthenticated(false);

  await tester.pumpWidget(makeTestableWidget(child: MainAppBar(title: 'Test')));

  var icon = find.byIcon(Icons.logout);
  await tester.tap(icon);
  await tester.pump();

  verifyNever(mockAuthProvider.signOut());
});

testWidgets('Clicking on logout icon calls signOut if user is '
  'authenticated AND push replace route', 
  (WidgetTester tester) async {
      
  setIsAuthenticated(true);

  await tester.pumpWidget(makeTestableWidget(child: MainAppBar(title: 'Test')));

  var icon = find.byIcon(Icons.logout);
  await tester.tap(icon);
  await tester.pumpAndSettle();

  verify(mockAuthProvider.signOut());
  verify(mockObserver.didPush(any, any));
  expect(find.text('Login'), findsOneWidget);
});