flutter_gherkin #

A fully featured Gherkin parser and test runner. Works with Flutter and Dart 2.

This implementation of the Gherkin tries to follow as closely as possible other implementations of Gherkin and specifically Cucumber in it's various forms.

  # Comment
  Feature: Addition

    @tag
    Scenario: 1 + 0
      Given I start with 1
      When I add 0
      Then I end up with 1

    Scenario: 1 + 1
      Given I start with 1
      When I add 1
      Then I end up with 2

Table of Contents #

flutter_gherkin

Getting Started #

See https://docs.cucumber.io/gherkin/ for information on the Gherkin syntax and Behaviour Driven Development (BDD).

See example readme for a quick start guide to running the example features and app.

The first step is to create a version of your app that has flutter driver enabled so that it can be automated. A good guide how to do this is show here. However in short, create a folder called test_driver and within that create a file called app.dart and paste in the below code.

import '../lib/main.dart';
import 'package:flutter/widgets.dart';
import 'package:flutter_driver/driver_extension.dart';

void main() {
  // This line enables the extension
  enableFlutterDriverExtension();

  // Call the `main()` function of your app or call `runApp` with any widget you
  // are interested in testing.
  runApp(new MyApp());
}

All this code does is enable the Flutter driver extension which is required to be able to automate the app and then runs your application.

To get started with BDD in Flutter the first step is to write a feature file and a test scenario within that.

First create a folder called test_driver (this is inline with the current integration test as we will need to use the Flutter driver to automate the app). Within the folder create a folder called features, then create a file called counter.feature.

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

  Scenario: Counter increases when the button is pressed
    Given I expect the "counter" to be "0"
    When I tap the "increment" button 10 times
    Then I expect the "counter" to be "10"

Now we have created a scenario we need to implement the steps within. Steps are just classes that extends from the base step definition class or any of its variations Given, Then, When, And, But.

Granted the example is a little contrived but is serves to illustrate the process.

This library has a couple of built in step definitions for convenience. The first step uses the built in step, however the second step When I tap the "increment" button 10 times is a custom step and has to be implemented. To implement a step we have to create a simple step definition class.

import 'package:flutter_driver/flutter_driver.dart';
import 'package:flutter_gherkin/flutter_gherkin.dart';

class TapButtonNTimesStep extends When2WithWorld<String, int, FlutterWorld> {
  @override
  Future<void> executeStep(String input1, int input2) async {
    final locator = find.byValueKey(input1);
    for (var i = 0; i < input2; i += 1) {
      await world.driver.tap(locator);
    }
  }

  @override
  RegExp get pattern => RegExp(r"I tap the {string} button {int} times");
}

As you can see the class inherits from When2WithWorld and specifies the types of the two input parameters. The third type FlutterWorld is a special Flutter context object that allow access to the Flutter driver instance within the step. If you did not need this you could inherit from When2 which does not type the world context object but still provides two input parameters.

The input parameters are retrieved via the pattern regex from well know parameter types {string} and {int} explained below. They are just special syntax to indicate you are expecting a string and an integer at those points in the step text. Therefore, when the step to execute is When I tap the "increment" button 10 times the parameters "increment" and 10 will be passed into the step as the correct types. Note that in the pattern you can use any regex capture group to indicate any input parameter. For example the regex RegExp(r"When I tap the {string} (button|icon) {int} times") indicates 3 parameters and would match to either of the below step text.

When I tap the "increment" button 10 times    // passes 3 parameters "increment", "button" & 10
When I tap the "increment" icon 2 times       // passes 3 parameters "increment", "icon" & 2

It is worth noting that this library does not rely on mirrors (reflection) for many reasons but most prominently for ease of maintenance and to fall inline with the principles of Flutter not allowing reflection. All in all this make for a much easier to understand and maintain code base as well as much easier debugging for the user. The downside is that we have to be slightly more explicit by providing instances of custom code such as step definition, hook, reporters and custom parameters.

Now that we have a testable app, a feature file and a custom step definition we need to create a class that will call this library and actually run the tests. Create a file called app_test.dart and put the below code in.

import 'dart:async';
import 'package:glob/glob.dart';
import 'package:flutter_gherkin/flutter_gherkin.dart';

Future<void> main() {
  final config = FlutterTestConfiguration()
    ..features = [Glob(r"test_driver/features/**/*.feature")]
    ..reporters = [ProgressReporter()]
    ..restartAppBetweenScenarios = true
    ..targetAppPath = "test_driver/app.dart"
    ..exitAfterTestRun = true;
  return GherkinRunner().execute(config);
}

This code simple creates a configuration object and calls this library which will then promptly parse your feature files and run the tests. The configuration file is important and explained in further detail below. However, all that is happening is a Glob is provide which specifies the path to one or more feature files, it sets the reporter to the ProgressReporter report which mean prints to the result of a scenario and step to the standard output (console). Finally it specifies the path to the testable app created above test_driver/app.dart. This is important as it instructions the library which app to run the tests against.

Finally to actually run the tests run the below on the command line:

dart test_driver/app_test.dart

To debug tests see Debugging.

Note: You might need to ensure dart is accessible by adding it to your path variable.

Configuration #

The configuration is an important piece of the puzzle in this library as it specifies not only what to run but classes to run against in the form of steps, hooks and reporters. Unlike other implementation this library does not rely on reflection so need to be explicitly told classes to use.

The parameters below can be specified in your configuration file:

features

Required

An iterable of Glob patterns that specify the location(s) of *.feature files to run.

tagExpression

Defaults to null.

An infix boolean expression which defines the features and scenarios to run based of their tags. See Tags.

order

Defaults to ExecutionOrder.random

The order by which scenarios will be run. Running an a random order may highlight any inter-test dependencies that should be fixed.

stepDefinitions

Defaults to Iterable<StepDefinitionBase>

Place instances of any custom step definition classes Given, Then, When, And, But that match to any custom steps defined in your feature files.

import 'dart:async';
import 'package:glob/glob.dart';
import 'package:flutter_gherkin/flutter_gherkin.dart';
import 'steps/given_I_pick_a_colour_step.dart';
import 'steps/tap_button_n_times_step.dart';

Future<void> main() {
  final config = FlutterTestConfiguration()
    ..features = [Glob(r"test_driver/features/**/*.feature")]
    ..reporters = [StdoutReporter()]
    ..stepDefinitions = [TapButtonNTimesStep(), GivenIPickAColour()]
    ..restartAppBetweenScenarios = true
    ..targetAppPath = "test_driver/app.dart"
    ..exitAfterTestRun = true;
  return GherkinRunner().execute(config);
}

customStepParameterDefinitions

Defaults to CustomParameter<dynamic>.

Place instances of any custom step parameters that you have defined. These will be matched up to steps when scenarios are run and their result passed to the executable step. See Custom Parameters.

import 'dart:async';
import 'package:glob/glob.dart';
import 'package:flutter_gherkin/flutter_gherkin.dart';
import 'steps/colour_parameter.dart';
import 'steps/given_I_pick_a_colour_step.dart';
import 'steps/tap_button_n_times_step.dart';

Future<void> main() {
  final config = FlutterTestConfiguration()
    ..features = [Glob(r"test_driver/features/**/*.feature")]
    ..reporters = [StdoutReporter()]
    ..stepDefinitions = [TapButtonNTimesStep(), GivenIPickAColour()]
    ..customStepParameterDefinitions = [ColourParameter()]
    ..restartAppBetweenScenarios = true
    ..targetAppPath = "test_driver/app.dart"
    ..exitAfterTestRun = true;
  return GherkinRunner().execute(config);
}

hooks

Hooks are custom bits of code that can be run at certain points with the test run such as before or after a scenario. Place instances of any custom Hook class instance in this collection. They will then be run at the defined points with the test run. See Hooks.

reporters

Required

Reporters are classes that are able to report on the status of the test run. This could be a simple as merely logging scenario result to the console. There are a number of built-in reporter:

StdoutReporter : Logs all messages from the test run to the standard output (console).
ProgressReporter : Logs the progress of the test run marking each step with a scenario as either passed, skipped or failed.

You should provide at least one reporter in the configuration otherwise it'll be hard to know what is going on.

Note: Feel free to PR new reporters!

import 'dart:async';
import 'package:glob/glob.dart';
import 'package:flutter_gherkin/flutter_gherkin.dart';
import 'steps/colour_parameter.dart';
import 'steps/given_I_pick_a_colour_step.dart';
import 'steps/tap_button_n_times_step.dart';

Future<void> main() {
  final config = FlutterTestConfiguration()
    ..features = [Glob(r"test_driver/features/**/*.feature")]
    ..reporters = [StdoutReporter()]
    ..stepDefinitions = [TapButtonNTimesStep(), GivenIPickAColour()]
    ..customStepParameterDefinitions = [ColourParameter()]
    ..restartAppBetweenScenarios = true
    ..targetAppPath = "test_driver/app.dart"
    ..exitAfterTestRun = true;
  return GherkinRunner().execute(config);
}

createWorld

Defaults to null.

While it is not recommended so share state between steps within the same scenario we all in fact live in the real world and thus at time may need to share certain information such as login credentials etc for future steps to use. The world context object is created once per scenario and then destroyed at the end of each scenario. This configuration property allows you to specify a custom World class to create which can then be accessed in your step classes.

import 'dart:async';
import 'package:glob/glob.dart';
import 'package:flutter_gherkin/flutter_gherkin.dart';
import 'steps/colour_parameter.dart';
import 'steps/given_I_pick_a_colour_step.dart';
import 'steps/tap_button_n_times_step.dart';

Future<void> main() {
  final config = FlutterTestConfiguration()
    ..features = [Glob(r"test_driver/features/**/*.feature")]
    ..reporters = [StdoutReporter()]
    ..stepDefinitions = [TapButtonNTimesStep(), GivenIPickAColour()]
    ..customStepParameterDefinitions = [ColourParameter()]
    ..createWorld = (TestConfiguration config) async => await createMyWorldInstance(config)
    ..restartAppBetweenScenarios = true
    ..targetAppPath = "test_driver/app.dart"
    ..exitAfterTestRun = true;
  return GherkinRunner().execute(config);
}

exitAfterTestRun

Defaults to true

True to exit the program after all tests have run. You may want to set this to false during debugging.

Flutter specific configuration options #

The FlutterTestConfiguration will automatically create some default Flutter options such as well know step definitions, the Flutter world context object which provides access to a Flutter driver instance as well as the ability to restart you application under test between scenarios. Most of the time you should use this configuation object if you are testing Flutter applications.

restartAppBetweenScenarios

Defaults to true.

To avoid tests starting on an app changed by a previous test it is suggested that the Flutter application under test be restarted between each scenario. While this will increase the execution time slightly it will limit tests failing because they run against an app changed by a previous test. Note in more complex application it may also be necessary to use the AfterScenario hook to reset the application to a base state a test can run on. Logging out for example if restarting an application will present a lock screen etc.

targetAppPath

Defaults to lib/test_driver/app.dart

This should point to the testable application that enables the Flutter driver extensions and thus is able to be automated. This application wil be started when the test run in started and restarted if the restartAppBetweenScenarios configuration property is set to true.

Features Files #

Steps Definitions #

Step definitions are the coded representation of a textual step in a feature file. Each step starts with either Given, Then, When, And or But. It is worth noting that all steps are actually the same but semantically different. The keyword is not taken into account when matching a step. Therefore the two below steps are actually treated the same and will result in the same step definition being invoked.

Note: Step definitions (in this implementation) are allowed up to 5 input parameters. If you find yourself needing more than this you might want to consider making your step more isolated or using a Table parameter.

Given there are 6 kangaroos
Then there are 6 kangaroos

However, the domain language you choose will influence what keyword works best in each context. For more information https://docs.cucumber.io/gherkin/reference/#steps.

Given

Given steps are used to describe the initial state of a system. The execution of a Given step will usually put the system into well defined state.

To implement a Given step you can inherit from the Given class.

Given Bob has logged in

Would be implemented like so:

import 'package:flutter_gherkin/flutter_gherkin.dart';

class GivenWellKnownUserIsLoggedIn extends Given1<String> {
  @override
  Future<void> executeStep(String wellKnownUsername) async {
    // implement your code
  }

  @override
  RegExp get pattern => RegExp(r"(Bob|Mary|Emma|Jon) has logged in");
}

If you need to have more than one Given in a block it is often best to use the additional keywords And or But.

Given Bob has logged in
And opened the dashboard

Then

Then steps are used to describe an expected outcome, or result. They would typically have an assertion in which can pass or fail.

Then I expect 10 apples

Would be implemented like so:

import 'package:flutter_gherkin/flutter_gherkin.dart';

class ThenExpectAppleCount extends Then1<int> {
  @override
  Future<void> executeStep(int count) async {
    // example code
    final actualCount = await _getActualCount();
    expectMatch(actualCount, count);
  }

  @override
  RegExp get pattern => RegExp(r"I expect {int} apple(s)");
}

Caveat: The expect library currently only works within the library's own test function blocks; so using it with a Then step will cause an error. Therefore, the expectMatch or expectA or this.expect methods have been added which mimic the underlying functionality of except in that they assert that the give is true. The Matcher within Dart's test library still work and can be used as expected.

Step Timeout

By default a step will timeout if it exceed the defaultTimeout parameter in the configuration file. In some cases you want have a step that is longer or shorter running and in the case you can optionally proved a custom timeout to that step. To do this pass in a Duration object in the step's call to super.

For example, the below sets the step's timeout to 10 seconds.

import 'package:flutter_driver/flutter_driver.dart';
import 'package:flutter_gherkin/flutter_gherkin.dart';

class TapButtonNTimesStep extends When2WithWorld<String, int, FlutterWorld> {
  TapButtonNTimesStep()
      : super(StepDefinitionConfiguration()..timeout = Duration(seconds: 10));

  @override
  Future<void> executeStep(String input1, int input2) async {
    final locator = find.byValueKey(input1);
    for (var i = 0; i < 10; i += 1) {
      await world.driver.tap(locator, timeout: timeout);
    }
  }

  @override
  RegExp get pattern => RegExp(r"I tap the {string} button {int} times");
}

Multiline Strings

Multiline strings can follow a step and will be give to the step it proceeds as the final argument. To denote a multiline string the pre and postfix can either be third double or single quotes """ ... """ or ''' ... '''.

For example:

Given I provide the following "review" comment
"""
Some long review comment.
That can span multiple lines

Skip lines

Maybe even include some numbers
1
2
3
"""

The matching step definition would then be:

import 'package:flutter_gherkin/flutter_gherkin.dart';

class GivenIProvideAComment extends Given2<String, String> {
  @override
  Future<void> executeStep(String commentType, String comment) async {
    // TODO: implement executeStep
  }

  @override
  RegExp get pattern => RegExp(r"I provide the following {string} comment");
}

Data tables

import 'package:flutter_gherkin/flutter_gherkin.dart';

/// This step expects a multiline string proceeding it
///
/// For example:
///
/// `Given I add the users`
///  | Firstname | Surname | Age | Gender |
///  | Woody     | Johnson | 28  | Male   |
///  | Edith     | Summers | 23  | Female |
///  | Megan     | Hill    | 83  | Female |
class GivenIAddTheUsers extends Given1<Table> {
  @override
  Future<void> executeStep(Table dataTable) async {
    // TODO: implement executeStep
    for (var row in dataTable.rows) {
      // do something with row
      row.columns.forEach((columnValue) => print(columnValue));
    }
  }

  @override
  RegExp get pattern => RegExp(r"I add the users");
}

Well known step parameters

In addition to being able to define a step's own parameters (by using regex capturing groups) there are some well known parameter types you can include that will automatically match and convert the parameter into the correct type before passing it to you step definition. (see https://docs.cucumber.io/cucumber/cucumber-expressions/#parameter-types).

In most scenarios theses parameters will be enough for you to write quite advanced step definitions.

Parameter Name	Description	Aliases	Type	Example
{word}	Matches a single word surrounded by a quotes	{word}, {Word}	String	`Given I eat a {word}` would match `Given I eat a "worm"`
{string}	Matches one more words surrounded by a quotes	{string}, {String}	String	`Given I eat a {string}` would match `Given I eat a "can of worms"`
{int}	Matches an integer	{int}, {Int}	int	`Given I see {int} worm(s)` would match `Given I see 6 worms`
{num}	Matches an number	{num}, {Num}, {float}, {Float}	num	`Given I see {num} worm(s)` would match `Given I see 0.75 worms`

Note that you can combine there well known parameters in any step. For example Given I {word} {int} worm(s) would match Given I "see" 6 worms and also match Given I "eat" 1 worm

Pluralisation

As the aim of a feature is to convey human readable tests it is often desirable to optionally have some word pluaralised so you can use the special pluralisation syntax to do simple pluralisation of some words in your step definition. For example:

The step string Given I see {int} worm(s) has the pluralisation syntax on the word "worm" and thus would be matched to both Given I see 1 worm and Given I see 4 worms.

Custom Parameters

While the well know step parameter will be sufficient in most cases there are time when you would want to defined a custom parameter that might be used across more than or step definition or convert into a custom type.

The below custom parameter defines a regex that matches the words "red", "green" or "blue". The matches word is passed into the function which is then able to convert the string into a Color object. The name of the custom parameter is used to identity the parameter within the step text. In the below example the word "colour" is used. This is combined with the pre / post prefixes (which default to "{" and "}") to match to the custom parameter.

import 'package:flutter_gherkin/flutter_gherkin.dart';

enum Colour { red, green, blue }

class ColourParameter extends CustomParameter<Colour> {
  ColourParameter()
      : super("colour", RegExp(r"red|green|blue", caseSensitive: true), (c) {
          switch (c.toLowerCase()) {
            case "red":
              return Colour.red;
            case "green":
              return Colour.green;
            case "blue":
              return Colour.blue;
          }
        });
}

The step definition would then use this custom parameter like so:

import 'package:flutter_gherkin/flutter_gherkin.dart';
import 'colour_parameter.dart';

class GivenIPickAColour extends Given1<Colour> {
  @override
  Future<void> executeStep(Colour input1) async {
    // TODO: implement executeStep
  }

  @override
  RegExp get pattern => RegExp(r"I pick a {colour}");
}

This customer parameter would be used like this: Given I pick the colour red. When the step is invoked the word "red" would matched and passed to the custom parameter to convert it into a Color object which is then finally passed to the step definition code as a Color object.

World Context (per test scenario shared state)

Assertions

Tags #

Tags are a great way of organising your features and marking them with filterable information. Tags can be uses to filter the scenarios that are run. For instance you might have a set of smoke tests to run on every check-in as the full test suite is only ran once a day. You could also use an @ignore or @todo tag to ignore certain scenarios that might not be ready to run yet.

You can filter the scenarios by providing a tag expression to your configuration file. Tag expression are simple infix expressions such as:

@smoke

@smoke and @perf

@billing or @onboarding

@smoke and not @ignore

You can even us brackets to ensure the order of precedence

@smoke and not (@ignore or @todo)

You can use the usual boolean statement "and", "or", "not"

Also see https://docs.cucumber.io/cucumber/api/#tags

Hooks #

A hook is a point in the execution that custom code can be run. Hooks can be run at the below points in the test run.

Before any tests run
After all the tests have run
Before each scenario
After each scenario

To create a hook is easy. Just inherit from Hook and override the method(s) that signifies the point in the process you want to run code at. Note that not all methods need to be override, just the points at which you want to run custom code.

import 'package:flutter_gherkin/flutter_gherkin.dart';

class HookExample extends Hook {
  /// The priority to assign to this hook.
  /// Higher priority gets run first so a priority of 10 is run before a priority of 2
  int get priority => 1;

  @override
  /// Run before any scenario in a test run have executed
  Future<void> onBeforeRun(TestConfiguration config) async {
    print("before run hook");
  }

  @override
  /// Run after all scenarios in a test run have completed
  Future<void> onAfterRun(TestConfiguration config) async {
    print("after run hook");
  }

  @override
  /// Run before a scenario and it steps are executed
  Future<void> onBeforeScenario(
      TestConfiguration config, String scenario) async {
    print("running hook before scenario '$scenario'");
  }

  @override
  /// Run after a scenario has executed
  Future<void> onAfterScenario(
      TestConfiguration config, String scenario) async {
    print("running hook after scenario '$scenario'");
  }
}

Finally ensure the hook is added to the hook collection in your configuration file.

import 'dart:async';
import 'package:glob/glob.dart';
import 'package:flutter_gherkin/flutter_gherkin.dart';
import 'hooks/hook_example.dart';
import 'steps/colour_parameter.dart';
import 'steps/given_I_pick_a_colour_step.dart';
import 'steps/tap_button_n_times_step.dart';

Future<void> main() {
  final config = FlutterTestConfiguration()
    ..features = [Glob(r"test_driver/features/*.feature")]
    ..reporters = [StdoutReporter()]
    ..hooks = [HookExample()]
    ..stepDefinitions = [TapButtonNTimesStep(), GivenIPickAColour()]
    ..customStepParameterDefinitions = [ColourParameter()]
    ..restartAppBetweenScenarios = true
    ..targetAppPath = "test_driver/app.dart"
    ..exitAfterTestRun = true;
  return GherkinRunner().execute(config);
}

Reporting #

A reporter is a class that is able to report on the progress of the test run. In it simplest form it could just print messages to the console or be used to tell a build server such as TeamCity of the progress of the test run. The library has a number of built in reporters.

StdoutReporter - prints all messages from the test run to the console.
ProgressReporter - prints the result of each scenario and step to the console - colours the output.

You can create your own custom reporter by inheriting from the base Reporter class and overriding the one or many of the methods to direct the output message. The Reporter defines the following methods that can be overridden. All methods must return a Future<void> and can be async.

onTestRunStarted
onTestRunFinished
onFeatureStarted
onFeatureFinished
onScenarioStarted
onScenarioFinished
onStepStarted
onStepFinished
onException
message
dispose

Once you have created your custom reporter don't forget to add it to the reporters configuration file property.

Note: PR's of new reporters are always welcome.

Flutter #

Restarting the app before each test #

By default to ensure your app is in a consistent state at the start of each test the app is shut-down and restarted. This behaviour can be turned off by setting the restartAppBetweenScenarios flag in your configuration object. Although in more complex scenarios you might want to handle the app reset behaviour yourself; possibly via hooks.

You might additionally want to do some clean-up of your app after each test by implementing an onAfterScenario hook.

Flutter World

Pre-defined Steps #

For convenience the library defines a number of pre-defined steps so you can get going much quicker without having to implement lots of step classes. The pre-defined steps are:

Step Text	Description	Examples
I tap the {string} [button\|element\|label\|icon\|field\|text\|\widget]	Taps the element with the provided key ( given by the first input parameter)	`When I tap the "login" button`, `Then I tap the "save" icon`
I fill the {string} field with {string}	Fills the element with the provided key with the given value (given by the second input parameter)	`When I fill the "email" field with "someone@gmail.com"`
I expect the {string} to be {string}	Asserts that the element with the given key has the given string value	`Then I expect the "cost" to be "£10.95"`
I (open\|close) the drawer	Opens or closes the application default drawer	`When I open the drawer`, `And I close the drawer`
I pause for {int} seconds	Pauses the test execution for the given seconds. Only use in debug scenarios or to inspect the state of the app	`Then I pause for 20 seconds`

Flutter Driver Utilities

For convenience the library provides a static FlutterDriverUtils class that abstracts away some common Flutter driver functionality like tapping a button, getting and entering text, checking if an element is present or absent. See lib/src/flutter/utils/driver_utils.dart.

Debugging #

In VSCode simply add add this block to your launch.json file (if you testable app is called app_test.dart and within the test_driver folder, if not replace that with the correct file path). Don't forget to put a break point somewhere!

{
  "name": "Debug Features Tests",
  "request": "launch",
  "type": "dart",
  "program": "test_driver/app_test.dart",
  "flutterMode": "debug"
}

After which the file will most likely look like this

{
  // Use IntelliSense to learn about possible attributes.
  // Hover to view descriptions of existing attributes.
  // For more information, visit: https://go.microsoft.com/fwlink/?linkid=830387
  "version": "0.2.0",
  "configurations": [
    {
      "name": "Flutter",
      "request": "launch",
      "type": "dart"
    },
    {
      "name": "Debug Features Tests",
      "request": "launch",
      "type": "dart",
      "program": "test_driver/app_test.dart",
      "flutterMode": "debug"
    }
  ]
}

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