A BDD-oriented widget test runner using Cucumber. Use all the power and flexibility of the gherkin package with flutter test widget.

Write your own steps using gherkin syntax in .feature files, then create associated step definitions, set up the configuration and you are ready to describe actions and assertions of your application's widgets.


Table of Contents


-- Features

  • Run your tests written with gherkin within a widget test context,
  • Expose a CucumberWorld named WidgetCucumberWorld designed for widget tests with its buckets to store and share data through steps,
  • ✨ Accessibility-friendly : search widget by semantic labels AND check its full semantic,
  • Provide a Json loader to help building widget using Json data,
  • Screenshot and widget tree dumped in a file on test failure,
  • Gherkin reporters adapted for widget tests,

-- Getting started

Knowledge on Gherkin syntax and Cucumber framework helps, documentation available here: https://cucumber.io/docs/gherkin/.

This README is based on some gherkin README examples.

πŸ₯’ Add gherkin_widget_extension dependency

In the pubspec.yaml of your project, add the gherkin_widget_extension library in dev_dependencies :

gherkin_widget_extension: ^0.0.2

Then run pub get to download the dependency.

✏️ Write a scenario

In the test folder, create a features folder. If there is no test folder, then create it. In the features folder, create a feature file such as counter.feature and write your first scenario:

Feature: Counter
  The counter should be incremented when the button is pressed.

  @my_tag
  Scenario: Counter increases when the button is pressed
    Given I launch the counter application
    When I tap the "increment" button 10 times
    Then I expect the "counter" to be "10"

Next step: implementation of step definitions.

πŸ”— Declare step definitions

Step definitions are like links between the gherkin sentence and the code that interacts with the widget. Usually given steps are used to set up the test context, when step(s) represents the main action of the test (When the user validates the form, When the user applies his choice, ...) and the then steps assert everything assertable on the screen (text, state, semantics, ...).

In the test folder, create a step_definitions folder and within this folder, create a steps.dart file and start implementing step definitions:

import 'package:gherkin/gherkin.dart';
import 'package:gherkin_widget_extension/gherkin_widget_extension.dart';

StepDefinitionGeneric<WidgetCucumberWorld> givenAFreshApp() {
  return given<WidgetCucumberWorld>(
      'I launch the counter application', (context) async {
    // ...
  });
}

πŸ’‘ Advice

For better understanding, one of good practices advises to split step definitions files according to gherkin keywords (all Given step definitions within the same file given_steps.dart, all When step definitions within the same file when_steps.dart, etc...). Organizing those files into folders representing the feature is a plus.

βš™οΈ Add some configuration

The gherkin offers a wide list of customizable properties available here.

Within the folder test, create a new file named test_setup.dart to declare your own test configuration :

TestConfiguration TestWidgetsConfiguration({
  String featurePath = '*.feature',
}) {
  return TestConfiguration()
    ..features = [Glob(featurePath)]
    ..hooks = [WidgetHooks(dumpFolderPath: 'widget_tests_report_folder')]
    ..order = ExecutionOrder.sequential
    ..stopAfterTestFailed = false
    ..reporters = [
      WidgetStdoutReporter(),
      WidgetTestRunSummaryReporter(),
      XmlReporter(dirRoot: Directory.current.path)
    ]
    ..stepDefinitions = [
      givenAFreshApp(),
      whenButtonTapped(),
      thenCounterIsUpdated()
    ]
    ..defaultTimeout =
    const Duration(milliseconds: 60000 * 10);
}

More explanation about those options here.

Package distinctive features

..hooks

The package provides a hook class WidgetHooks which implements the Hook class supplied by the gherkin package. This class handles the widget test reporting such as screenshot and widget tree rendering.

More information here.

..reporters

Reporters provided by the gherkin package have been enriched in this package:

  • WidgetStdoutReporter: prints each gherkin step with its status in terminal logs
  • WidgetTestRunSummaryReporter: prints the summary of the entire test execution in the terminal log at the end of test execution.
  • XmlReporter: generates a XML test execution report in XML format, useful for GitLab CI tests reporting.

More information here.

πŸ§ͺ Set up the test runner

Create a new file widget_test_runner.dart in the test folder and call the test runner method:

void main() {
  testWidgetsGherkin('widget tests',
      testConfiguration: TestWidgetsConfiguration(featurePath: "test/features/*.feature"));
}

Create another file named flutter_test_config.dart in the test folder and declare the test executing configuration to enable font loading (required for screenshots):

Future<void> testExecutable(FutureOr<void> Function() testMain) async {
  await loadAppFonts();
  await testMain();
}

πŸͺ„ Run your tests

Open a terminal and execute the file you created before:

flutter test test/widget_test_runner.dart

You should see these kind of logs:

🎬️ Let's go!

Write as many gherkin scenarii as you need, play with cucumber tags to run some of your scenarii, and explore all options the gherkin package supply.


-- Usage

This package adds various options to the base package gherkin in order to make the test automation easier. Below the list and explanations of those new features.

🌎 WidgetCucumberWorld advantages

The gherkin package exposes a CucumberWorld to store data and share them with all the steps within the same scenario. A CucumberWorld is unique: there is only one per scenario, freshly created at the beginning and destroyed once the scenario is done, no matter its status. You will find more information about the goal of the CucumberWorld here.

The class WidgetCucumberWorld inherits from the CucumberWorld class of the gherkin package and exposes the following items:

  • WidgetTester tester: allows to interact with the widget (tap, pump, get elements, ...),
  • SemanticsHandle semantics: created at the beginning of the test, enables interactions with the Semantic widget,
  • String scenarioName: stores the current scenario name - used for reporting,
  • String json: stores the Json data used to build the widget,
  • Bucket bucket: stores test data coming from the steps variables, more information in the next paragraph.

No need to create a WidgetCucumberWorld object, the package provides one named currentWorld, accessible from the context object:

context.world.tester;

πŸͺ£ Buckets for data

If CucumberWorld were the test's backpack, Buckets would be its pockets.

Buckets allows you to organize your data in the CucumberWorld. Indeed, if your application has divergent use cases, such as tickets sells, customer account or traffic information, etc., you might not want to store all test data together within the CucumberWorld: you may use Buckets to store data according to their business domain (ex: TicketSellBucket, AccountBucket, ...).

Buckets are abstract and generic, so to use them, you need to create a class which implements the Bucket class:

class ExampleBucket implements Bucket {
  String? buttonAction;
  int nbActions = 0;
}

In this example, the bucket name is ExampleBucket and stores two values: the name of the button to interact with, and the number of times it was tapped.

Before storing data into a Bucket, it requires to be initialized through the WidgetCucumberWorld object named currentWorld:

currentWorld.bucket = ExampleBucket();

Then use currentWorld for setting and accessing to the Bucket's data:

currentWorld.readBucket<ExampleBucket>().nbActions = count;

Keep in mind that bucket type is required to use it and access to its data (here <ExampleBucket>).

πŸ‘οΈ Don't forget the accessibility

Accessibility is essential in mobile application and must be tested as well. This package provides a method to test widget semantics:

Finder widgetWithSemanticLabel(
Type widgetType,
    String semanticLabel,
{bool skipOffstage = true,
Matcher? semanticMatcher}
)

This method allows you to find a widget by its type, its semantic label and its full semantics:


final widgetToFind = find.widgetWithSemanticLabel(Checkbox, "Checkbox label",
    semanticMatcher: matchesSemantics(
        hasEnabledState: true,
        label: "Checkbox label",
        hasTapAction: true,
        isEnabled: true,
        isFocusable: true,
        textDirection: TextDirection.ltr,
        hasCheckedState: true,
        isChecked: true));

expect(widgetToFind, findsOneWidget);

The expect raises an AssertionError if no corresponding widget exists.

πŸ”„ Loading data for widgets with JsonLoader

Applications often use data coming from an API to build components in its screens and widget test cannot depend on API and its potential slowness and instabilities. Widgets tests are expected to be reliable and as fast as possible. This way, API Json responses can be stored into files and loaded through the provided JsonLoader to help building the widget to test.

var jsonMap = await JsonLoader.loadJson("path/to/json/folder");

jsonMap contains a map where keys are json filenames and values the json files content.

πŸ“Έ A Hook for screenshot and widget tree rendering

πŸ“£ At least one font must be declared in the pubspec.yml to have nice and understandable screenshots (Squares will replace fonts otherwise).

πŸ“£ The flutter_test_config.dart must exist at the root of test directory ( See πŸ§ͺ Set up the test runner paragraph).

Hooks contain methods executed before or after specific milestones during a test driven by Cucumber (before/after scenario, before/after steps, ...). More information about Hooks here.

This package supplies a Hook named WidgetHooks to improve reporting and provide more information on test failure such as screenshots and widget tree rendering. Add this Hook in your TestConfiguration to enjoy its features :

TestConfiguration()
..hooks = [WidgetHooks(dumpFolderPath: 'widget_tests_report_folder')]

Parameter dumpFolderPath is mandatory: it represents the report folder where screenshots and widget rendering will be stored on test failure.

πŸ“£ This package provides a custom Widget called MaterialTestWidget. This widget must encapsulate the widget to pump to enable screenshots and widget rendering.

πŸ“‹ Widget test reporters

The package includes several reporters optimized for widget tests and a custom log printer.

MonochromePrinter

This class extends the LogPrinter class and simplifies the logging. It is the base of the other provided reporters. Flutter logger is really nice and handy but can be too verbose in reporting context. The MonochromePrinter allows you to print your message in the log console without any decorations/emojis/whatever.

WidgetStdoutReporter

This reporter is in charge of:

  • printing the name of the running scenario with its file location,
  • printing each step with its status and time duration
    • √ if step succeeded
    • Γ— if step failed
    • - if step skipped
  • printing the scenario execution result
    • PASSED
    • FAILED
  • handling text coloration

Example:

WidgetTestRunSummaryReporter

This reporter is in charge of printing the test execution summary and its text coloration. It sums up:

  • the total number of expected scenarii
  • the total number of passed scenarii
  • the total number of failed scenarii
  • the total number of skipped scenarii

Example:

XmlReporter

This reporter generates a XML file named junit-report.xml in JUnit format, understandable by GitLab CI. This file is created in the root directory. This way, all test execution results will appear in the Tests tab of the pipeline:

The details for each test execution is also available:

On failure, the System output contains:

  • a recap of steps with their status (passed, failed or skipped)
  • stacktrace of the exception
  • print of the widget rendering

On failure, a link to the screenshot is also provided.

🦊 Take care with GitLab Job configuration: expose screenshots and XML file as artifacts to allow GitLab CI to gather information in the Tests tab. More information about GitLab Tests Report here.

Add reporters in test configuration

To benefit from supplied reporters, they need to be added on the TestConfiguration:

TestConfiguration()
..reporters = [
WidgetStdoutReporter(),
WidgetTestRunSummaryReporter(),
XmlReporter(dirRoot: Directory.current.path)
]