dart test

Learn the dart test framework.

The dart test framework

dart test is Dart's built-in test framework. Tests live in the test/ folder with the *_test.dart extension. They run from the command line with dart test.

A test file starts with import 'package:test/test.dart';. Each test is written as test('description', () { ... }). Inside it you make claims with expect.

Tests verify that your code behaves as expected. A wrong change turns a test red, so you catch the error early.

The test file skeleton

A test file skeleton looks like this: it starts with import 'package:test/test.dart';, then test('addition', () { expect(2 + 3, equals(5)); });. Here expect compares the actual and expected values.

equals(5) is a matcher. The expected value is 5; the actual value is 2 + 3 = 5. If equal the test is green, otherwise red.

Each test should be short and probe one behavior. The description tells what is being probed.

Exercise The Calculator class

Define a Calculator class with a method int add(int a, int b) => a + b;. In main print the result of Calculator().add(2, 3) with print.

Show example solution

class Calculator {
  int add(int a, int b) => a + b;
}

void main() {
  print(Calculator().add(2, 3));
}

Test yourself

What does the dart test command run?
- The lib/ folder
- pubspec.yaml
- The bin/ folder
- The *_test.dart files in test/
Show answer

The *_test.dart files in test/ — dart test runs the *_test.dart files inside test/.

Import the test package

import 'package:test/____.dart';

Show answer

import 'package:test/test.dart';

Test file parts

test/

Test folder
*_test.dart

Test file name
import 'package:test/test.dart'

Import
test('...', () {})

Test block

Next lesson: test and expect

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