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Test a ViewModel

ViewModels in code_on_the_rocks are state objects so in order to test them, you need to build the corresponding StatefulWidget (ex. for the CounterViewModel, you need to build the CounterViewModelBuilder).

void main() {
  testWidgets('CounterViewModel smoke test', (WidgetTester tester) async {
    await tester.pumpWidget(MaterialApp(builder: (context, child) => const CounterView()));
  });
}

Once the ViewModelBuilder widget is added to the tree, you can use the state method on WidgetTester to find the state object:

final CounterViewModel model = tester.state(find.byType(CounterViewModelBuilder));

With the model in hand, you can start test it's internal logic directly:

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

    // Action - Act
    model.increment();

    // Result - Assert
    expect(model.counter, 1);

    model.decrement();
    expect(model.counter, 0);
  });
}