Test a ViewModelBuilder

ViewModelBuilders are StatefulWidgets which means they need to be tested using the WidgetTester. They can be tested like any other widget as shown here.

  testWidgets('CounterViewModel UI test', (WidgetTester tester) async {
    // Setup - Arrange
    await tester.pumpWidget(MaterialApp(builder: (context, child) => const CounterView()));
    final CounterViewModel model = tester.state(find.byType(CounterViewModelBuilder));

    // finders
    final counterFinder = find.text('Counter');
    final incrementFinder = find.byIcon(Icons.add);
    final decrementFinder = find.byIcon(Icons.remove);

    expect(counterFinder, findsOneWidget);
    expect(incrementFinder, findsOneWidget);
    expect(decrementFinder, findsOneWidget);
  });

You can update the model directly to verify that the UI updates appropriately:

  testWidgets('CounterViewModel UI test', (WidgetTester tester) async {
    // Setup - Arrange
    await tester.pumpWidget(MaterialApp(builder: (context, child) => const CounterView()));
    final CounterViewModel model = tester.state(find.byType(CounterViewModelBuilder));

    model.setState(() => model.counter = 7);

    await tester.pump();

    // finders
    final countFinder = find.text('7');

    expect(countFinder, findsOneWidget);
  });