require_mirror_test

v1.1.0WarningConfigurableTesting Rules

Warns when a library under lib/ has no matching test file:

lib/src/core/version.dart   ->   test/src/core/version_test.dart
lib/parser.dart             ->   test/parser_test.dart

The message says a test file is missing, not that the code is untested — the rule cannot tell the difference.

This rule is in no preset. Whether a project mirrors its test tree is a project decision, so it must be enabled by name.

many_lints:
  rules:
    require_mirror_test: true

rules:
  require_mirror_test: true

Don’t

// lib/src/core/version.dart — with no test/src/core/version_test.dart
class Version {
  const Version(this.major, this.minor);

  final int major;
  final int minor;
}

Do

class Version {
  const Version(this.major, this.minor);

  final int major;
  final int minor;
}

void main() {
  test('parses a two-part version', () {
    expect(Version.parse('1.2'), equals(const Version(1, 2)));
  });
}

Examples

Defaults: `test/`, `_test.dart`

require_mirror_test: true

lib/parser.dart              ->  test/parser_test.dart
lib/src/core/version.dart    ->  test/src/core/version_test.dart
lib/src/net/http_client.dart ->  test/src/net/http_client_test.dart

A project whose tests live elsewhere

Both the directory and the suffix are configurable — a package using spec/ and _spec.dart names them:

analysis_options.yaml
many_lints.yaml

many_lints:
  rules:
    require_mirror_test:
      test_dir: spec
      suffix: _spec

rules:
  require_mirror_test:
    test_dir: spec
    suffix: _spec

lib/src/core/version.dart    ->  spec/src/core/version_spec.dart

Accepting a test that moved

By default a file of the right name satisfies the rule wherever it sits under the test directory, so reorganising the test tree does not light up the whole package:

fallback_anywhere: true   # the default

lib/src/core/version.dart
  satisfied by test/src/core/version_test.dart   (the mirrored path)
  satisfied by test/unit/version_test.dart       (found by the fallback)

Set it to false when the exact mirrored path is itself the convention you want enforced:

analysis_options.yaml
many_lints.yaml

many_lints:
  rules:
    require_mirror_test:
      fallback_anywhere: false

rules:
  require_mirror_test:
    fallback_anywhere: false

lib/src/core/version.dart
  satisfied by test/src/core/version_test.dart
  NOT satisfied by test/unit/version_test.dart   // LINT

Exempting a layer

exclude takes globs. Public barrels at the root of lib/, or a directory of generated adapters, are typical exemptions:

analysis_options.yaml
many_lints.yaml

many_lints:
  rules:
    require_mirror_test:
      exclude:
        - 'lib/*.dart'
        - 'lib/src/adapters/**'

rules:
  require_mirror_test:
    exclude:
      - 'lib/*.dart'
      - 'lib/src/adapters/**'

Files that are never reported

These need no configuration:

// lib/src/models/user.g.dart      — generated, skipped
// lib/generated/l10n.dart         — under generated/, skipped

// lib/src/models/models.dart — a barrel: exports only, so nothing to test
export 'user.dart';
export 'order.dart';

// lib/src/util/_helpers.dart — nothing public, so no surface a test can target
String _slugify(String value) => value.toLowerCase();

// lib/src/core/version_impl.dart — a part file; its library is checked instead
part of 'version.dart';

A file that both exports and declares is not a barrel — it has code of its own, so it is still reported.

Options

Option	Type	Default	Description
`test_dir`	string	`test`	The directory the mirrored path is rooted at
`suffix`	string	`_test`	Appended to the file’s base name
`fallback_anywhere`	bool	`true`	Accept a file of the right name anywhere under `test_dir`

Known limitations

It checks for a file, not for tests. An empty version_test.dart satisfies the rule. Coverage tooling answers the other half.

Only lib/. Code under bin/, tool/ or example/ is never reported.

Names, not contents, under fallback_anywhere. With the default on, any version_test.dart anywhere under test/ satisfies every version.dart in the package, including one in a different directory.

Turning this rule off

rules:
  require_mirror_test: false

To keep the rule on but skip certain paths, use per-rule exclude.

avoid_misused_test_matchers — Detect test matchers used with incompatible value types.
format_test_name — Hold test descriptions to a house pattern.
prefer_correct_test_file_name — Name test files so the runner actually runs them.
prefer_test_matchers — Prefer using a Matcher instead of a literal value in expect().