Guide Flutter · 5/6

Testing

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Flutter ships its testing tools with the SDK. Tests fall into three groups by scope: unit tests check a single function or class, widget tests check a widget or a small part of a screen, and integration tests run the whole app on a real device or emulator. The broader the test, the more realistic and the slower it is, so write many unit and widget tests and keep integration tests for critical flows.

Kind	Scope	Runs on	Speed
Unit test	Functions, classes, state logic	Dart VM	Very fast
Widget test	Widgets, parts of screens	Simulated test environment	Fast
Integration test	Full app flows	Device, emulator or desktop	Slow

Unit tests

Put test files in the test folder and end their names with _test.dart. In Flutter projects, the flutter_test package also provides test, group and expect.

// lib/cart.dart
class Cart {
  final Map<String, int> _prices = {};

  void add(String name, int price) => _prices[name] = price;
  int get total => _prices.values.fold(0, (sum, price) => sum + price);
}

// test/cart_test.dart
import 'package:flutter_test/flutter_test.dart';
import 'package:hello_app/cart.dart';

void main() {
  group('Cart', () {
    test('starts with a total of 0', () {
      expect(Cart().total, 0);
    });

    test('adding items increases the total', () {
      final cart = Cart()
        ..add('apple', 1000)
        ..add('pear', 2500);
      expect(cart.total, 3500);
    });
  });
}

Run tests from the command line or your editor:

# Run all tests
flutter test

# Run a single file
flutter test test/cart_test.dart

# Run tests whose name matches
flutter test --name "total"

# Collect coverage (writes coverage/lcov.info)
flutter test --coverage

Widget tests use testWidgets. The WidgetTester mounts a widget (pumpWidget), finds things (find), interacts (tap), rebuilds (pump) and then you assert. The generated test/widget_test.dart is exactly this kind of test:

import 'package:flutter/material.dart';
import 'package:flutter_test/flutter_test.dart';
import 'package:hello_app/main.dart';

void main() {
  testWidgets('tapping add increments the counter', (WidgetTester tester) async {
    await tester.pumpWidget(const MyApp());

    expect(find.text('0'), findsOneWidget);
    expect(find.text('1'), findsNothing);

    await tester.tap(find.byIcon(Icons.add));
    await tester.pump();

    expect(find.text('0'), findsNothing);
    expect(find.text('1'), findsOneWidget);
  });
}

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Testing

Unit tests

Widget tests

Replacing dependencies

Integration tests

Summary

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