Migrating Dart Tests to Package Checks

Contents

• Dependency Management
• Syntax Migration Guidelines
• Utilizing Dart MCP Tools
• Migration Workflow
• Examples

Dependency Management

Manage dependencies using the Dart Tooling MCP Server pub tool or standard CLI commands.

• Add package:checks as a dev_dependency using dart pub add dev:checks.
• Remove package:matcher if it is explicitly listed in the pubspec.yaml (note: it is often transitively included by package:test, which is fine).
• Import package:checks/checks.dart in all test files undergoing migration.

Syntax Migration Guidelines

Transition test assertions from the package:matcher syntax to the literate API provided by package:checks.

• Basic Equality: Replace expect(actual, equals(expected)) or expect(actual, expected) with check(actual).equals(expected).
• Type Checking: Replace expect(actual, isA<Type>()) with check(actual).isA<Type>().
• Property Extraction: Replace expect(actual.property, expected) with check(actual).has((a) => a.property, 'property name').equals(expected).
• Cascades for Multiple Checks: Use Dart's cascade operator (..) to chain multiple expectations on a single subject.
• Asynchronous Expectations:
  • If checking a Future, await the check call: await check(someFuture).completes((r) => r.equals(expected));.
  • If checking a Stream, wrap it in a StreamQueue for multiple checks, or use .withQueue for single/broadcast checks.

Utilizing Dart MCP Tools

Leverage the Dart MCP Server tools to automate and validate the migration process.

• Use pub to run dart pub get or dart pub add.
• Use analyze_files to run static analysis on the project or specific paths.
• Use run_tests to execute Dart or Flutter tests with an agent-centric UX. ALWAYS use this instead of shell commands like dart test.
• Use dart_fix to apply automated fixes if applicable.

Migration Workflow

Copy and use the following checklist to track progress when migrating a test suite:

• Task Progress
  • Add package:checks as a dev dependency.
  • Identify all test files using package:matcher (expect calls).
  • Import package:checks/checks.dart in target test files.
  • Rewrite all expect(...) statements to check(...) statements.
  • Run static analyzer (analyze_files).
  • Run tests (run_tests).

Feedback Loop: Static Analysis

1. Run the analyze_files tool on the modified test directories.
2. Review any static analysis warnings or errors (e.g., missing imports, incorrect generic types on isA, unawaited futures).
3. Fix the warnings.
4. Repeat until the analyzer returns zero issues.

Feedback Loop: Test Validation

1. Run the run_tests tool.
2. If tests fail, review the failure output. package:checks provides detailed context (e.g., Which: has length of <2>).
3. Adjust the check() expectations or the underlying code to resolve the failure.
4. Repeat until all tests pass.

Examples

Basic Assertions

Input (matcher):

expect(someList.length, 1);
expect(someString, startsWith('a'));
expect(someObject, isA<Map>());

Output (checks):

check(someList).length.equals(1);
check(someString).startsWith('a');
check(someObject).isA<Map>();

Composed Expectations

Input (matcher):

expect('foo,bar,baz', allOf([
  contains('foo'),
  isNot(startsWith('bar')),
  endsWith('baz')
]));

Output (checks):

check('foo,bar,baz')
  ..contains('foo')
  ..not((s) => s.startsWith('bar'))
  ..endsWith('baz');

Asynchronous Futures

Input (matcher):

expect(Future.value(10), completion(equals(10)));
expect(Future.error('oh no'), throwsA(equals('oh no')));

Output (checks):

await check(Future.value(10)).completes((it) => it.equals(10));
await check(Future.error('oh no')).throws<String>().equals('oh no');

Asynchronous Streams

Input (matcher):

var stdout = StreamQueue(Stream.fromIterable(['Ready', 'Go']));
await expectLater(stdout, emitsThrough('Ready'));

Output (checks):

var stdout = StreamQueue(Stream.fromIterable(['Ready', 'Go']));
await check(stdout).emitsThrough((it) => it.equals('Ready'));