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prefer-test-matchers

added in: 1.6.0
warning
Pro+

Warns when the second argument of an expect or expectLater is not a subclass of a Matcher.

Even though matchers might require more code to write, they produce a more readable message when a test fails.

Example​

❌ Bad:

void main() {
  final array = [1, 2, 3];

  expect(array.length, 1); // LINT: Prefer test matchers instead of literal values.
  expectLater(array.length, 1); // LINT: Prefer test matchers instead of literal values.

  const value = 'hello';
  expect(value is String, isTrue); // LINT: Prefer the 'isA<T>' matcher instead of the 'is T' check.
}

✅ Good:

void main() {
  final array = [1, 2, 3];

  expect(array, hasLength(1));
  expectLater(array, hasLength(1));

  const value = 'hello';
  expect(value, isA<String>());
}