dart-collect-coverage

Implementing Dart and Flutter Test Coverage

Contents

• Testing Fundamentals
• Coverage Directives
• Workflow: Configuring and Generating Coverage Reports
• Workflow: Advanced Manual Coverage Collection
• Examples

Testing Fundamentals

Structure your test suites using the standard Dart testing paradigms. Use package:test for Dart projects and flutter_test for Flutter projects.

• Unit Tests: Verify individual functions, methods, or classes.
• Component/Widget Tests: Verify component behavior, layout, and interaction using mock objects (package:mockito).
• Integration Tests: Verify entire app flows on simulated or real devices.

Coverage Directives

Exclude specific lines, blocks, or entire files from coverage metrics using inline comments. Pass the --check-ignore flag during formatting to enforce these directives.

• Ignore a single line: // coverage:ignore-line
• Ignore a block of code: // coverage:ignore-start and // coverage:ignore-end
• Ignore an entire file: // coverage:ignore-file

Workflow: Configuring and Generating Coverage Reports

Follow this sequential workflow to add the coverage package, execute tests, and generate an LCOV report.

Task Progress Checklist:

• 1. Add coverage as a dev_dependency.
• 2. Execute the automated coverage script.
• 3. Validate the LCOV output.

1. Add Dependencies

Add the coverage package as a dev_dependency to your project. Do not add it to standard dependencies.

If working in a standard Dart project:

dart pub add dev:coverage

If working in a Flutter project:

flutter pub add dev:coverage

2. Collect Coverage and Generate LCOV

Use the bundled test_with_coverage script. This script automatically runs all tests, collects the JSON coverage data from the Dart VM, and formats it into an LCOV report.

dart run coverage:test_with_coverage

Note: If working within a Dart workspace (monorepo), specify the test directories explicitly (e.g., dart run coverage:test_with_coverage -- pkgs/foo/test pkgs/bar/test).

3. Feedback Loop: Validate Output

Run validator -> review errors -> fix:

1. Verify that the coverage/ directory was created in the project root.
2. Ensure coverage/coverage.json (raw data) and coverage/lcov.info (formatted report) exist.
3. If coverage is missing for specific files, ensure they are imported and executed by your test files, or add // coverage:ignore-file if they are intentionally excluded.

Workflow: Advanced Manual Coverage Collection

If you require granular control over the VM service, isolate pausing, or need branch/function-level coverage, use the manual collection workflow.

Task Progress Checklist:

• 1. Run tests with VM service enabled.
• 2. Collect raw JSON coverage.
• 3. Format JSON to LCOV.

1. Run Tests with VM Service

Execute tests while pausing isolates on exit and exposing the VM service on a specific port (e.g., 8181).

2. Collect Raw Coverage

Extract the coverage data from the running VM service and output it to a JSON file.

Optional: Append --function-coverage and --branch-coverage to gather deeper metrics (requires Dart VM 2.17.0+).

3. Format to LCOV

Convert the raw JSON data into the standard LCOV format.

Examples

Example: pubspec.yaml Configuration

Ensure your pubspec.yaml reflects the coverage package strictly under dev_dependencies.

Example: Applying Ignore Directives

Use ignore directives to prevent generated code or untestable edge cases from lowering coverage scores.