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A gherkin unit test framework based on flutter's official flutter_test package.

🧪 Gherkin Unit Test #

This package is based on the Behaviour Driven Development (BDD) language called Gherkin. This language enables us as developers to design and execute tests in an intuitive and readable way. For people who have a little less experience with development, these tests are also easy to understand because the syntax is very similar to English.

Most tests look something like this:

Feature: This feature shows an example

    Scenario: It shows a good example
      Given we start without an example
      When an example gets created
      Then the example should explode

In this same way we have built our framework, we have the following classes at our disposal:

  • UnitTest
  • UnitFeature
  • UnitScenario
  • UnitExample
  • UnitStep (abstract)
    • Given
    • When
    • Then
    • And
    • But

From top to bottom, each class may contain a number of the class below it (one to many). A UnitTest may contain multiple UnitFeature which in turn may contain multiple UnitScenario which in turn may contain multiple UnitExample and UnitStep.

🛠 Implementation #


Start by creating a test class that inherits the UnitTest class. Then create a constructor that takes no arguments but does call the superclass with a description and (for now) an empty list of features.

class DummyUnitTest extends UnitTest {
  DummyUnitTest()
      : super(
          description: 'All unit tests regarding dummies',
          features: [],
        );
}

📲 Features #


In the features list we can now define our first UnitFeature. We give it a name and (for now) an empty list of scenarios.

The UnitFeature is also the place where we (for this example) define the systemUnderTest that we would like to test.

This paramater takes a callback where you may perform any logic to initialise the systemUnderTest. This callback is carried out after before any setUp methods you specify in that class.

In this example we’ll use a DummyService() as our systemUnderTest. The DummyService gets a dummyMock as its parameter which we will save to the UnitMocks object so we can later manipulate it as we see fit.

class DummyUnitTest extends UnitTest {
  DummyUnitTest()
      : super(
          description: 'All unit tests regarding dummies',
          features: [
            UnitFeature<DummyService>(
              description: 'Saving of dummies',
              setUpMocks: (mocks) {
                mocks.write(DummyMock());
              },
              systemUnderTest: (mocks) {
                return DummyService(dummyDependency: mocks.read(DummyMock));
              },
              scenarios: [],
            ),
          ],
        );
}

🤝 Scenarios #


Now it's time to think about what kind of scenarios might occur in your test. For this example we will use ’a successful save’ and ‘an unsuccessful save’ as possible scenarios.

We use the UnitScenario class to create both scenarios and place them in the empty list. We also pass in a description and this time an empty list of steps.

class DummyUnitTest extends UnitTest {
  DummyUnitTest()
      : super(
          description: 'All unit tests regarding dummies',
          features: [
            UnitFeature<DummyService>(
              description: 'Saving of dummies',
              setUpMocks: (mocks) {
                mocks.write(DummyMock());
              },
              systemUnderTest: (mocks) {
                return DummyService(dummyDependency: mocks.read(DummyMock));
              },
              scenarios: [
                UnitScenario(
                  description: 'Saving a good dummy should succeed',
                  steps: [],
                ),
                UnitScenario(
                  description: 'Saving a bad dummy should fail',
                  steps: [],
                ),
              ],
            ),
          ],
        );
}

🐾 Steps #


Now comes the good part. For each scenario, we may define steps. We have access to Given, When, Then, And and But. All of these steps do basically the same thing in the background, but by using them correctly, you learn to plan, work out and execute your tests in an intuitive and proper BDD way.

Each step requires a description and a callback. The callback for the UnitTests looks as follows and grants access to the following parameters:

/// Callback used to provide the necessary tools to execute an [UnitStep].
typedef UnitStepCallback<SUT, Example extends UnitExample?> = FutureOr<void> Function(
  SUT systemUnderTest,
  UnitLog log,
  UnitBox box,
  UnitMocks mocks, [
  Example? example,
]);
  • SUT systemUnderTest

    • The class that we specified earlier in the UnitScenario that resembles the unit that we want to test.
  • Log log

    • Class that allows for subtle logging of steps information in your tests.
  • UnitBox box

    • This box is basically a map that may be used to write and read values that need to persist throughout a series of steps inside a UnitScenario. Any value that you box.write(key, value) will be retrievable in all UnitStep's after that or until removed or until all steps have been executed. Reading a value with box.read(key) will automatically cast it to the Type that you specify. So reading an int like this → final int value = box.read(myIntValue) would automatically cast it to an int (🆒).

      Using the box may look like this:

      [
        Given(
          'This is an example for the UnitBox',
          (systemUnderTest, log, box, mocks, [example]) {
            box.write('isExample', true);
          },
        ),
        When(
          'we write some values',
          (systemUnderTest, log, box, mocks, [example]) {
            box.write('exampleValue', 1);
            box.write('mood', 'happy');
          },
        ),
        Then(
          'all the values should be accessible up until the last step.',
          (systemUnderTest, log, box, mocks, [example]) {
            final bool isExample = box.read('isExample');
            final int exampleValue = box.read('exampleValue');
            final bool mood = box.read('mood');
            expect(isExample, true);
            expect(exampleValue, 1);
            expect(mood, 'happy');
          },
        ),
      ]
      
  • UnitMocks mocks

    • A box that exists and persists throughout your entire UnitTest, UnitFeature and/or UnitScenario. You may have optionally use this box to store mocks that you need so you may later retrieve them to stub methods to your liking.
  • UnitExample? example

    • Optional ‘Scenario Outline’ examples that may have been specified inside a UnitScenario like this:

      UnitScenario(
        description: 'Saving a good dummy should succeed',
        examples: [
          const UnitExample(values: [1]),
          const UnitExample(values: [5]),
          const UnitExample(values: [10]),
        ],
      )
      

      This UnitScenario will now run 3 times, once for each UnitExample. You may access the example in the following way:

      Given(
        'I access the example value',
        (systemUnderTest, log, box, mocks, [example]) {
          final int exampleValue = example!.firstValue();
        },
      )
      

🐾 Steps Implementation #

Combining all that information will allow us to finalise and set up the success scenario like this:

class DummyUnitTest extends UnitTest {
  DummyUnitTest()
      : super(
          description: 'All unit tests regarding dummies',
          features: [
            UnitFeature<DummyService>(
              description: 'Saving of dummies',
              setUpMocks: (mocks) {
                mocks.write(DummyMock());
              },
              systemUnderTest: (mocks) {
                return DummyService(dummyDependency: mocks.read(DummyMock));
              },
              scenarios: [
                UnitScenario(
                  description: 'Saving a good dummy should succeed',
                  steps: [
                    Given(
                      'The dummy service is initialised',
                      (systemUnderTest, log, box, mocks, [_]) {
												mocks.read(DummyMock).stubWhatever();
                        // TODO(you): Initialise service
                      },
                    ),
                    When(
                      'We call the dummy service with dummy info',
                      (systemUnderTest, log, box, mocks, [example]) {
                        // TODO(you): Call dummy service with dummy info
                      },
                    ),
                    Then(
                      'It should succeed',
                      (systemUnderTest, log, box, mocks, [example]) {
                        // TODO(you): Verify success
                      },
                    ),
                  ],
                ),
                UnitScenario(
                  description: 'Saving a bad dummy should fail',
                  steps: [],
                ),
              ],
            ),
          ],
        );
}

🏆 Bonus UnitSteps #


Because not everybody wants to write tests the same way we also created these combined step classes to allow for creating the same kind of unit tests, but with less steps.

  • GivenWhenThen
    • For when you can’t be bothered to create and use the separate step functionality regarding the ‘Given’, ‘When’ and ‘Then’ steps. This allows you to write the entire test in one step.
  • WhenThen
    • For when you can’t be bothered to create and use the separate step functionality regarding the ‘When’ and ‘Then’ steps. This allows you to combine both steps into one.
  • Should
    • For when you feel like using steps is not your style. This step defines the entire test in one ‘Should’ sentence.

⚡️ Almost there! #

While this may perfectly fit our testing needs there are a couple functionalities at our disposal that give our tests extra power.

🏗 setUpOnce, setUpEach, tearDownOnce, tearDownEach #


Each class has access to these methods and will run them in sort of the same way:

  • setUpEach - will run at the START of EACH UnitScenario under the chosen class (may be specified in UnitTestUnitFeature or UnitScenario itself).
  • tearDownEach - will run at the END of EACH UnitScenario under the chosen class (may be specified in UnitTestUnitFeature or UnitScenario itself).
  • setUpOnce - will run ONCE at the START of chosen class (may be specified in UnitTestUnitFeature or UnitScenario itself).
  • tearDownOnce - will run ONCE at the END of chosen class (may be specified in UnitTestUnitFeature or UnitScenario itself).

Using the methods may look a bit like this:

class DummyUnitTest extends UnitTest {
  DummyUnitTest()
      : super(
          description: 'All unit tests regarding dummies',
          setUpOnce: (mocks, systemUnderTest) async {
            await AppSetup.initialise(); // Runs once at the start of this test.
          },
          setUpEach: (mocks, systemUnderTest) async {
            systemUnderTest.reset();
          },
          tearDownOnce: (mocks, systemUnderTest) async {
            await AppSetup.dispose(); // Runs once at the end of this test.
          },
          features: [
            UnitFeature<DummyService>(
              description: 'Saving of dummies',
              setUpEach: (mocks, systemUnderTest) {
                // TODO(you): Do something
              },
              setUpMocks: (mocks) {
                mocks.write(DummyMock());
              },
              systemUnderTest: (mocks) {
                return DummyService(dummyDependency: mocks.read(DummyMock));
              },
              scenarios: [
                UnitScenario(
                  description: 'Saving a good dummy should succeed',
                  tearDownEach: (mocks, systemUnderTest) {
                    // TODO(you): Do something
                  },
                  examples: [
                    const UnitExample(values: [1]),
                    const UnitExample(values: [5]),
                    const UnitExample(values: [10]),
                  ],
                  steps: [
                    Given(
                      'I access the example value',
                      (systemUnderTest, log, box, mocks, [example]) {
                        final int exampleValue = example!.firstValue();
                      },
                    )
                  ],
                ),
                UnitScenario(
                  description: 'Saving a bad dummy should fail',
                  steps: [],
                ),
              ],
            ),
          ],
        );
}

✅ Success! #

Now to run these tests all you have to do is add the DummyUnitTests to your main test function, hit run and pray for success.

void main() {
  DummyUnitTests().test();
}
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A gherkin unit test framework based on flutter's official flutter_test package.

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Documentation

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License

BSD-3-Clause (LICENSE)

Dependencies

flutter, flutter_test, integration_test

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