prefer_test_matchers

v0.4.0 Warning Testing Rules

Flags expect() and expectLater() calls where the second argument is a raw literal value instead of a Matcher subclass. Using raw literals like expect(x, 1) produces less informative failure messages than using matchers like expect(x, equals(1)).

Why use this rule

When a test fails, matchers provide descriptive output such as “Expected: has length of 3 / Actual: [1, 2]” instead of just “Expected: 3 / Actual: 2”. This makes debugging faster. Using matchers also enables richer assertions like hasLength(), contains(), and isA<T>() that raw values cannot express.

See also: test package - Matchers

Don’t

expect(array.length, 1);
expect(value, 'hello');
expect(true, true);
expect(array, [1, 2, 3]);
expect(maybeNull, null);
expectLater(array.length, 1);

Do

expect(array, hasLength(1));
expect(value, equals('hello'));
expect(true, isTrue);
expect(array, equals([1, 2, 3]));
expect(maybeNull, isNull);
expect(value, isA<String>());
expectLater(array, hasLength(3));

Configuration

To disable this rule:

plugins:
  many_lints:
    diagnostics:
      prefer_test_matchers: false