Test Harness

A package to help with the creation of test harnesses to allow better readability and composability of tests

Uses Given, When, then, but unlike a lot of other test frameworks there is a single callback.

based on the ebay given_when_then, but exposes setup in creation of hte harness which allows mixin or inheritance to reuse test setup/teardown code.

Installation 💻

Add test_harness to your pubspec.yaml:

dev_dependencies:
  widget_test_harness: ^0.7.1

Install it:

flutter packages get

Harness setup

Harnesses are setup by subclassing an appropriate harness class widgetTestHarness and unitTestHarness.

Below is a basic example that has the included NetworkImageMixin which is used to mock the network image requests.

import 'package:widget_test_harness/widget_test_harness.dart';

final class ExampleWidgetTestHarness extends WidgetTestHarness
    with NetworkImageMixin, CounterHarnessMixin {
  ExampleWidgetTestHarness(super.tester);

  @override
  List<int> bytesForUrlRequest(Uri url) {
    final file = File('test/test_resources/sunflower.jpg');
    final bytes = file.readAsBytesSync();
    return bytes;
  }
}

The harness is passed into Given, When, Then and extensions off of each can define methods.

extension MyGivenForExample on Given<ExampleWidgetTestHarness> {
  Future<void> setupWidget() async {...}
}
extension MyWhenForExample on When<ExampleWidgetTestHarness> {
  Future<void> userPerformsSomeAction() {}
}

Writing Mixins

Using mixins different features can be reused throughout an application's test code.

base mixin CounterHarnessMixin on FlutterTestHarness {
  CounterModel counter = CounterModel();
  @override
  Widget setupWidgetTree(Widget child) {
    return super.setupWidgetTree(Provider.value(value: counter, child: child));
  }
}
extension CounterHarnessGiven on Given<CounterHarnessMixin> {
  void countIs(int value) {}
}
extension CounterHarnessThen on Then<CounterHarnessMixin> {
  void countEquals(int value) => expect(value,harness.counter.value);
}

Writing Tests

Writing a test invokes a function that will create the harness and setup state for that individual test. You should never have to use setup(), or teardown() while using a test harness.

final uiHarness = HarnessSetup.setupWidgetHarness(ExampleWidgetTestHarness.new);

void main() {
   testWidgets('test Counter', uiHarness((given, when, then) async {
      given.countIs(1);
      await given.setupWidget();
      await when.userPerformsSomeAction();
      await then.findsWidgetText();
      then.countEquals(2);
    }));
}

-- see example_test.dart for additional example of usage

Libraries

widget_test_harness