Widget Testing With Flutter: Getting Began

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On this tutorial about Widget Testing with Flutter, you’ll discover ways to guarantee UI widgets look and behave as anticipated by writing check code.

Replace notice: Stephanie Patterson up to date this tutorial for Flutter 3.3 and Dart 2.18. Lawrence Tan wrote the unique.

Testing is necessary throughout your app growth. As your product grows, it will get extra advanced, and performing guide exams turns into tougher. Having an automatic testing atmosphere helps optimize this course of.

Widget testing is like UI testing: You develop the feel and appear of your app, guaranteeing each interplay the consumer makes produces the anticipated outcome.

For this tutorial, you’ll write widget exams for a automotive app referred to as Drive Me, which lets customers view a listing of vehicles, view particulars about them and choose and consider particular vehicles. Within the course of, you’ll discover ways to check that the app correctly performs the next capabilities:

  • Hundreds mock knowledge to the widget exams.
  • Injects inaccurate mock knowledge for adverse exams.
  • Ensures that the app presents a listing of sorted vehicles and shows its particulars.
  • Checks that the automotive choice seems appropriately within the checklist web page.
  • Ensures that the automotive particulars web page shows appropriately.

Getting Began

To begin, obtain the starter mission by clicking the Obtain Supplies button on the high or backside of the tutorial, then discover the starter mission in Visible Studio Code. You can even use Android Studio, however this tutorial makes use of Visible Studio Code in its examples.

Make certain to run flutter packages get both on the command line or when prompted by your IDE. This pulls the newest model of the packages wanted for this mission.

Notice: Within the starter mission, you’ll seemingly see warnings about Unused import or variables not getting used. Ignore these as they are going to be used by the point you have got accomplished this tutorial.

Construct and run the mission with flutter run to familiarize your self with how the app works.

Car list

Exploring the Starter Venture

The starter mission contains the implementation of the app so you may concentrate on widget testing. Check out the contents in lib to grasp how the app works.

Project Structure

Beginning on the backside, as you recognize most important.dart is the file the place all Flutter apps begin. dependency_injector.dart is the place the app registers the principle knowledge layer courses and injects them by way of get_it.

constants.dart comprises many of the variables you’ll use all through the app.

The mission has 4 most important folders:

  • database
  • particulars
  • checklist
  • fashions

Within the lib/fashions folder, you’ll discover an necessary file. automotive.dart is the place the Automobile() and CarsList() mannequin implementations reside. The CarsList() mannequin holds a listing of vehicles and an error message if an exception happens.

Subsequent, have a look at lib/checklist/cars_list_bloc.dart. That is the CarsList() knowledge layer. CarsListBloc masses knowledge from the JSON present in belongings/sample_data/knowledge.json and passes it to the widget checklist. Thereafter, it types the vehicles alphabetically by way of alphabetizeItemsByTitleIgnoreCases().

Within the lib/particulars folder is car_details_bloc.dart, which will get knowledge from CarsListBloc and passes it to the CarDetails widget in car_details_page.dart.

Open lib/particulars/car_details_page.dart. You’ll see that on init it retrieves the info handed in by CarDetailsBloc and presents it on the widget. When customers choose or deselect objects, CarsListBloc() makes the updates.

When the consumer selects any automotive, a separate knowledge stream manages it.

lib/database comprises cars_database.dart, which implements an summary class referred to as CarsDataProvider. This class comprises loadCars() that parses the JSON file containing a listing of automotive knowledge. The parsed knowledge returned is a CarsList().

As you guessed it from some filenames, this mission makes use of BLoC to move knowledge between the widgets layer and the info layer.

Now that you simply’ve tried the app and perceive the implementation particulars, it’s time to start out operating some exams.

Earlier than you dive deep into the subject of widget testing with Flutter, take a step again and examine it with unit testing.

Unit Testing vs. Widget Testing

Unit Testing vs Widget Testing

Unit testing is a course of the place you examine for high quality, efficiency or reliability by writing additional code that ensures your app logic works as anticipated. It exams for logic written in capabilities and strategies. The unit exams then develop and accumulate to cowl a whole class and subsequently an enormous a part of the mission, if not all.

The objective of a widget check is to confirm that each widget’s UI seems to be and behaves as anticipated. Essentially, you carry out exams by re-rendering the widgets in code with mock knowledge.

This additionally tells you that should you modify the logic of the app — for instance, you modify the login validation of the username from a minimal of six characters to seven — then your unit check and widget check might each fail collectively.

Assessments lock down your app’s options, which provide help to to correctly plan your app’s design earlier than growing it.

Testing Pyramid

There are three sorts of exams you may carry out with Flutter:

  • Unit exams: Used to check a way or class.
  • Widget exams: These check a single widget.
  • Integration exams: Use these to check the important flows of the whole app.

So, what number of exams will you want? To determine, check out the testing pyramid. It summarizes the important sorts of exams a Flutter app ought to have:

Testing Pyramid

Basically, unit exams ought to cowl many of the app, then widget exams and, lastly, integration exams.

Even when good testing grounds are in place, you shouldn’t omit guide testing.

As you go up the pyramid, the exams get much less remoted and extra built-in. Writing good unit exams provide help to construct a powerful base to your app.

Now that you simply perceive the necessity for testing, it’s time to dive into the mission for this tutorial!

Widget Testing the Automobile Record

Open check/checklist/cars_list_bloc_test.dart. Look under // TODO 3: Unit Testing Information Loading Logic and also you’ll see the unit exams carried out on this mission. These unit exams be sure that the info construction you present to the widget is correct.

Earlier than going into writing the check scripts, it’s good to have a look at the precise display screen you’re testing. In check/database/mock_car_data_provider.dart, the consumer has chosen the primary automotive — the Hyundai Sonata 2017, proven the picture under:

Car List with selected card highlighted in blue

Are you prepared to start out including widget exams?

Your First Check

Open check/checklist/cars_list_page_test.dart and add the next beneath // TODO 4: Inject and Load Mock Automobile Information:


carsListBloc.injectDataProviderForTest(MockCarDataProvider());

That is injecting the mock automotive check knowledge into carsListBloc.

Beneath // TODO 5: Load & Kind Mock Information for Verification add:


last vehicles = await MockCarDataProvider().loadCars();
vehicles.objects.kind(carsListBloc.alphabetizeItemsByTitleIgnoreCases);

Right here you’re ready for the mock automotive knowledge to load after which kind the checklist.

Injecting check knowledge

Now it’s time to inject the check knowledge.

Add these traces of code under // TODO 6: Load and render Widget:


await tester.pumpWidget(const ListPageWrapper());
await tester.pump(Length.zero);

pumpWidget() renders and performs a runApp of a stateless ListPage widget wrapped in ListPageWrapper(). Then, you name pump() to render the body and specify how lengthy to attend. On this case you don’t desire a delay so Length.zero is used.

This prepares the widget for testing!

Notice: pumpWidget calls runApp, and in addition triggers a body to color the app. That is adequate in case your UI and knowledge are all supplied instantly from the app, or you would name them static knowledge (i.e., labels and texts).

When you have got a construction (i.e. checklist, collections) with repeated knowledge fashions, pump() turns into important to set off a rebuild because the data-loading course of will occur post-runApp.

Guaranteeing visibility

Beneath // TODO 7: Test Automobiles Record's part's existence by way of key to make sure that the Carslist is within the view add these traces of code:


last carListKey = discover.byKey(const Key(carsListKey));
count on(carListKey, findsOneWidget);

Should you have a look at lib/checklist/cars_list_page.dart, you will note that the widget tree identifies ListView() with a key referred to as carsListKey(). findsOneWidget makes use of a matcher to find precisely one such widget.

The mock knowledge in mock_car_data_provider.dart has a complete of six vehicles, however you don’t need to write a check for each. A very good follow is to make use of a for loop to iterate via and confirm every automotive on the checklist.

Return to check/checklist/cars_list_page_test.dart and under // TODO 8: Create a perform to confirm checklist's existence add this:


void _verifyAllCarDetails(
  Record<Automobile> carsList,
  WidgetTester tester,
) async {
  for (last automotive in carsList) {
    last carTitleFinder = discover.textual content(automotive.title);
    last carPricePerDayFinder = discover.textual content(
      pricePerDayText.replaceFirst(
        wildString,
        automotive.pricePerDay.toStringAsFixed(2),
      ),
    );
    await tester.ensureVisible(carTitleFinder);
    count on(carTitleFinder, findsOneWidget);
    await tester.ensureVisible(carPricePerDayFinder);
    count on(carPricePerDayFinder, findsOneWidget);
  }
}

This check verifies that the title and the worth per day show appropriately. That is potential due to a perform referred to as ensureVisible().

Car List with selected card highlighted in blue

To see extra about ensureVisible(), hover over it to see its description routinely displayed.

Popup showing ensureVisible definition

Notice: You wrap a ListView in a SingleChildScrollView to make this work in cars_list_page.dart. On the time of writing, you should do that for the check to move.

Theoretically, a ListView additionally comprises a scrollable ingredient to permit scrolling. The check doesn’t at present confirm photographs.

Testing photographs is pricey: It requires getting knowledge from the community and verifying chunks of knowledge. This may result in an extended check length because the variety of check instances will increase.

To confirm the automotive particulars, discover // TODO 9: Name Confirm Automobile Particulars perform and add this under it to name to the perform you simply created:


_verifyAllCarDetails(vehicles.objects, tester);

Within the subsequent part you’ll discover ways to add exams to confirm the chosen automotive has a blue background.

Widget Testing the Automobile Record Web page with Choice

Keep in mind when you choose a automotive it has a blue background? You must create a check to make sure that occurs.

Nonetheless in cars_list_page_test.dart, add this beneath // TODO 10: Choose a Automobile:


carsListBloc.selectItem(1);

The widget tester makes an attempt to pick out Automobile ID 1.

Discover // TODO 11: Confirm that Automobile is highlighted in blue add the next under it:


// 1
bool widgetSelectedPredicate(Widget widget) =>
          widget is Card && widget.shade == Colours.blue.shade200;
// 2
bool widgetUnselectedPredicate(Widget widget) =>
          widget is Card && widget.shade == Colours.white;

count on(
   discover.byWidgetPredicate(widgetSelectedPredicate),
   findsOneWidget,
);
count on(
  discover.byWidgetPredicate(widgetUnselectedPredicate),
  findsNWidgets(5),
);

Right here you have got created two predicates:

  1. Confirm the chosen card has a blue background
  2. Make sure the unselected card stays white

Run this check now. Hurray, your new check passes! :]

Selected cars background turns blue

You’re doing very properly. It’s time to strive some adverse exams earlier than ending with the testing of the automotive particulars web page.

Damaging Assessments for Automobile Record Web page

Now it’s time to check for errors. To simulate errors, add the next under // TODO 12: Inject and Load Error Mock Automobile Information:


carsListBloc.injectDataProviderForTest(MockCarDataProviderError());

You’ve injected knowledge earlier than. The one distinction right here is that you simply inject MockCarDataProviderError(), which comprises mock error knowledge.

Beneath // TODO 13: Load and render Widget add:


  await tester.pumpWidget(const ListPageWrapper());
  await tester.pump(Length.zero);

As earlier than, pumpWidget() and pump() set off a body to color and render instantly.

Beneath // TODO 14: Confirm that Error Message is proven add the next so as to add error messages.


last errorFinder = discover.textual content(
  errorMessage.replaceFirst(
    errorMessage,
    mockErrorMessage,
  ),
);
count on(errorFinder, findsOneWidget);

This replaces the errorMessage with the mockErrorMessage and confirms the error message shows.

Prepared to your fifth check? Run it.

Proper error message displayed

Nice job! Your fifth check handed!

Verifying view replace

There’s one final check it’s good to carry out for this widget, which is to confirm the widget updates its view if knowledge is available in after getting an error.

You must check in case your app doesn’t have any vehicles to show.

Carlist Error Data

Since this subsequent step contains code you’ve already used, you’re going to do a big replace directly. Discover and substitute // TODO Substitute testWidgets('''After encountering an error...''' and the whole placeholder testWidgets() beneath it with:


testWidgets(
    '''After encountering an error, and stream is up to date, Widget can be 
    up to date.''',
    (WidgetTester tester) async {
      // TODO 15: Inject and Load Error Mock Automobile Information
      carsListBloc.injectDataProviderForTest(MockCarDataProviderError());

      // TODO 16: Load and render Widget
      await tester.pumpWidget(const ListPageWrapper());
      await tester.pump(Length.zero);

      // TODO 17: Confirm that Error Message and Retry Button is proven
      last errorFinder = discover.textual content(
        errorMessage.replaceFirst(
          errorMessage,
          mockErrorMessage,
        ),
      );
      last retryButtonFinder = discover.textual content(retryButton);
      count on(errorFinder, findsOneWidget);
      count on(retryButtonFinder, findsOneWidget);

      // TODO 18: Inject and Load Mock Automobile Information
      carsListBloc.injectDataProviderForTest(MockCarDataProvider());
      await tester.faucet(retryButtonFinder);

      // TODO 19: Reload Widget
      await tester.pump(Length.zero);

      // TODO 20: Load and Confirm Automobile Information
      last vehicles = await MockCarDataProvider().loadCars();
      _verifyAllCarDetails(vehicles.objects, tester);
    },
  );

Right here’s what the code does:

  • TODO 15–17: These are the identical because the exams you probably did within the final step.
  • TODO 18: Injects automotive mock knowledge.
  • TODO 19: Reloads the widget.
  • TODO 20: Waits for mock dat to load after which verifies the automotive particulars.

Time to run the check. Run it now, and …

Proper error message shown

Superior work! Your sixth check passes!

You’ve examined for when a automotive is chosen. What about when it’s been deselected? You guessed it, that’s subsequent.

Widget Testing the Automobile Particulars Web page for the Deselected Automobile

Take one other have a look at the Automobile Particulars Web page. Right here is an instance of a particular automotive and one other that has not been chosen.

Selected and unselected cars

Discover how the title and button textual content are completely different relying on the consumer’s alternative. You must check for that.
Open check/particulars/car_details_page_test.dart add substitute // TODO Substitute testWidgets('Unselected Automobile Particulars Web page...' together with the corresponding placeholder testWidgets() code with this:


testWidgets(
    'Unselected Automobile Particulars Web page ought to be proven as Unselected',
    (WidgetTester tester) async {
      // TODO 21: Inject and Load Mock Automobile Information
      carsListBloc.injectDataProviderForTest(MockCarDataProvider());
      await carsListBloc.loadItems();

      // TODO 22: Load & Kind Mock Information for Verification
      last vehicles = await MockCarDataProvider().loadCars();
      vehicles.objects.kind(carsListBloc.alphabetizeItemsByTitleIgnoreCases);

      // TODO 23: Load and render Widget
      await tester.pumpWidget(
          const DetailsPageSelectedWrapper(2)); // Mercedes-Benz 2017
      await tester.pump(Length.zero);

      // TODO 24: Confirm Automobile Particulars
      last carDetailKey = discover.byKey(const Key(carDetailsKey));
      count on(carDetailKey, findsOneWidget);

      last pageTitleFinder =
          discover.textual content(vehicles.objects[1].title); // 2nd automotive in sorted checklist
      count on(pageTitleFinder, findsOneWidget);

      last notSelectedTextFinder = discover.textual content(notSelectedTitle);
      count on(notSelectedTextFinder, findsOneWidget);

      last descriptionTextFinder = discover.textual content(vehicles.objects[1].description);
      count on(descriptionTextFinder, findsOneWidget);

      last featuresTitleTextFinder = discover.textual content(featuresTitle);
      count on(featuresTitleTextFinder, findsOneWidget);

      last allFeatures = StringBuffer();
      for (last characteristic in vehicles.objects[1].options) {
        allFeatures.write('n $characteristic n');
      }

      last featureTextFinder = discover.textual content(allFeatures.toString());
      await tester.ensureVisible(featureTextFinder);
      count on(featureTextFinder, findsOneWidget);

      last selectButtonFinder = discover.textual content(selectButton);
      await tester.scrollUntilVisible(selectButtonFinder, 500.0);
      count on(selectButtonFinder, findsOneWidget);
    },
  );

Right here’s what you achieved with the code above:

  • TODO 21–23: As soon as once more, you inject, load and kind the info, then put together and pump the widget.
  • TODO 24: Should you open lib/particulars/car_details_page.dart, you’ll discover a widget that’s recognized with a key, a web page title, a deselected title, a options checklist and a selectButton. The code on this TODO lets you confirm these widgets! scrollUntilVisible() scrolls via the scrollable widget, in your app’s case the ListView widget, till the anticipated widget is discovered.

Time to run your exams.

Unselected cars should show unselecte

You’ve got created a wide range of exams. Nice job! Are you prepared for a problem?

Widget Testing Problem

Your problem is to make use of what you’ve study and full the ultimate exams by yourself. You are able to do it!

Should you get caught or need to examine options, simply click on the Reveal button. Give it a strive first. :]

Aims:

  1. The chosen Automobile Particulars Web page ought to present a static Chosen textual content on the high of the web page. When viewing a particular automotive, the main points web page ought to be represented appropriately.
  2. When choosing and deselecting a automotive, the main points web page ought to replace accordingly.
  3. The answer is damaged up into two exams. You’ll nonetheless be working in car_details_page_test.dart. Trace, TODO 25–28 and TODO 29–32 are listed within the mission.

[spoiler]

Testing Particulars Web page for Chosen Automobiles

TODO 25–28:


testWidgets(
    'Chosen Automobile Particulars Web page ought to be proven as Chosen',
    (WidgetTester tester) async {
      // TODO 25: Inject and Load Mock Automobile Information
      carsListBloc.injectDataProviderForTest(MockCarDataProvider());
      await carsListBloc.loadItems();

      // TODO 26: Load and render Widget
      await tester.pumpWidget(
          const DetailsPageSelectedWrapper(3)); // Hyundai Sonata 2017
      await tester.pump(Length.zero);

      // TODO 27: Load Mock Information for Verification
      last actualCarsList = await MockCarDataProvider().loadCars();
      last actualCars = actualCarsList.objects;

      // TODO 28: First Automobile is Chosen, so Confirm that
      last carDetailKey = discover.byKey(const Key(carDetailsKey));
      count on(carDetailKey, findsOneWidget);

      last pageTitleFinder = discover.textual content(actualCars[2].title);
      count on(pageTitleFinder, findsOneWidget);

      last notSelectedTextFinder = discover.textual content(selectedTitle);
      count on(notSelectedTextFinder, findsOneWidget);

      last descriptionTextFinder = discover.textual content(actualCars[2].description);
      count on(descriptionTextFinder, findsOneWidget);

      last featuresTitleTextFinder = discover.textual content(featuresTitle);
      count on(featuresTitleTextFinder, findsOneWidget);

      last actualFeaturesStringBuffer = StringBuffer();
      for (last characteristic in actualCars[2].options) {
        actualFeaturesStringBuffer.write('n $characteristic n');
      }

      last featuresTextFinder =
          discover.textual content(actualFeaturesStringBuffer.toString());
      await tester.ensureVisible(featuresTextFinder);
      count on(featuresTextFinder, findsOneWidget);

      last selectButtonFinder = discover.textual content(removeButton);
      //await tester.ensureVisible(selectButtonFinder);
      await tester.scrollUntilVisible(selectButtonFinder, 500.0);

      count on(selectButtonFinder, findsOneWidget);
    },
  );

Check that the Chosen Automobile Updates the Widget

TODO 29–32:


testWidgets(
    'Deciding on Automobile Updates the Widget',
    (WidgetTester tester) async {
      // TODO 29: Inject and Load Mock Automobile Information
      carsListBloc.injectDataProviderForTest(MockCarDataProvider());
      await carsListBloc.loadItems();

      // TODO 30: Load & Kind Mock Information for Verification
      last vehicles = await MockCarDataProvider().loadCars();
      vehicles.objects.kind(carsListBloc.alphabetizeItemsByTitleIgnoreCases);

      // TODO 31: Load and render Widget for the primary automotive
      await tester.pumpWidget(
          const DetailsPageSelectedWrapper(2)); // Mercedes-Benz 2017
      await tester.pump(Length.zero);

      // TODO 32: Faucet on Choose and Deselect to make sure widget updates
      last selectButtonFinder = discover.textual content(selectButton);
      await tester.scrollUntilVisible(selectButtonFinder, 500.0);
      await tester.faucet(selectButtonFinder);

      await tester.pump(Length.zero);

      last deselectButtonFinder = discover.textual content(removeButton);
      //await tester.ensureVisible(deselectButtonFinder);
      await tester.scrollUntilVisible(deselectButtonFinder, 500.0);

      await tester.faucet(deselectButtonFinder);

      await tester.pump(Length.zero);

      last newSelectButtonFinder = discover.textual content(selectButton);
      //await tester.ensureVisible(newSelectButtonFinder);
      await tester.scrollUntilVisible(newSelectButtonFinder, 500.0);

      count on(newSelectButtonFinder, findsOneWidget);
    },
  );

[/spoiler]

After you’ve completed your problem, rerun your exams. There are 9 exams they usually’ve all handed! :]

9 test passed

Congratulations! You’re now an official Widget Testing Ambassador, go forth and unfold the excellent news!

Flutter Widget Testing award

The place to Go From Right here?

Obtain the ultimate mission by clicking the Obtain Supplies button on the high or backside of this tutorial.

To your subsequent steps, increase your Flutter testing data by exploring the official UI exams cookbook from the Flutter crew.

Then take your testing to the following degree by exploring and integrating Mockito to mock dwell internet providers and databases.

We hope you loved this tutorial. When you’ve got any questions or feedback, please be a part of the discussion board dialogue under!

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