dart-test-coverage

--- name: dart-test-coverage description: |- Understand and improve test coverage in a Dart package. Helps agents run coverage, interpret results, and identify missed lines. key_features: - LCOV report collection - Missed line identification - Coverage analysis & improvement ---

# Dart Test Coverage

Guidelines for running and interpreting test coverage in Dart packages.

## When to use this skill - When asked to "check test coverage" or "improve coverage". - When you need to identify which parts of a library are untested.

## Discovery

To find areas lacking test coverage:

### Run Coverage Analysis Follow the workflow to generate and interpret coverage data: 1. **Run Tests with Coverage**: `dart test --coverage=.dart_tool/coverage` 2. **Interpret Results**: Use the script or `format_coverage` as described in the **Interpreting Results** section to identify specific files and missed lines.

## How to use this skill (The Workflow) 1. Ensure tests pass by running `dart test`. 2. Collect coverage by running `dart test --coverage=.dart_tool/coverage`. 3. Interpret the results using the provided script or standard tools. 4. Add tests to cover missed lines.

## Running Coverage Run the following command to collect coverage in JSON format: ```bash dart test --coverage=.dart_tool/coverage ```

> [!NOTE] > We use `.dart_tool/coverage` as the output directory because `.dart_tool` > is typically already ignored in `.gitignore` files.

> [!TIP] > For projects with complex conditional logic, you can pass the > `--branch-coverage` flag to `dart test` to collect branch-level coverage.

## Interpreting Results

### Option 1: Use the custom interpreter script This repository includes a zero-dependency script that parses the raw JSON output and provides a summary of covered percentage and missed lines.

Run it from the project root (adjust path to script as needed): ```bash dart run skills/dart-test-coverage/scripts/interpret_coverage.dart .dart_tool/coverage <package_name> ``` Replace `<package_name>` with the name from `pubspec.yaml`.

Example Output: ``` package:my_pkg/src/file.dart: 50.0% (2/4 lines) Missed lines: 3, 4 ```

### Option 2: Use package:coverage If `package:test` is installed, `package:coverage` is likely available as a transitive dependency. You can use its `format_coverage` tool.

To get a human-readable "pretty print" of the coverage: ```bash dart run coverage:format_coverage --in=.dart_tool/coverage --out=stdout --pretty-print --report-on=lib ``` This will output the file content with hit counts on the left (e.g., `0|` for missed lines).

## Best Practices for Reporting Results When presenting coverage results to the user, follow these guidelines: 1. **State the high-level percentage first** to give immediate context. 2. **Identify specific files and missed lines** clearly. 3. **Translate line numbers to code**: Don't just say "lines 3-6 are missed". Look at the source file and tell the user which functions or blocks are untested (e.g., "The `divide` function is missing coverage"). 4. **Propose concrete fixes**: Provide example test code that the user can immediately apply to cover the missed lines. 5. **Use tables for multi-file summaries**: When reporting on multiple files, use a markdown table with columns for File, Coverage %, and Missed Lines to make the summary easy to scan.

## Constraints - ALWAYS verify that tests pass before collecting coverage. - DO NOT commit the `.dart_tool/coverage` directory. - Focus coverage improvements on `lib/` files, not `test/` or generated files.