Test Coverage Expander

Expand unit test coverage by targeting untested branches and edge cases.

Repo Sync Before Edits (mandatory)

Before creating/updating/deleting files in an existing repository, sync the current branch with remote:

branch="$(git rev-parse --abbrev-ref HEAD)"
git fetch origin
git pull --rebase origin "$branch"

If the working tree is not clean, stash first, sync, then restore:

git stash push -u -m "pre-sync"
branch="$(git rev-parse --abbrev-ref HEAD)"
git fetch origin && git pull --rebase origin "$branch"
git stash pop

If origin is missing, pull is unavailable, or rebase/stash conflicts occur, stop and ask the user before continuing.

Workflow

0. Create Feature Branch

Before making any changes:

1. Check the current branch - if already on a feature branch for this task, skip
2. Check the repo for branch naming conventions (e.g., feat/, feature/, etc.)
3. Create and switch to a new branch following the repo's convention, or fallback to: feat/test-coverage

1. Analyze Coverage

Detect the project's test runner and run the coverage report:

• JavaScript/TypeScript: npx jest --coverage or npx vitest --coverage
• Python: pytest --cov=. --cov-report=term-missing
• Go: go test -coverprofile=coverage.out ./...
• Rust: cargo tarpaulin or cargo llvm-cov

From the report, identify:

• Untested branches and code paths
• Low-coverage files/functions (prioritize files below 60%)
• Missing error handling tests

2. Identify Test Gaps

Review code for:

• Logical branches (if/else, switch)
• Error paths and exceptions
• Boundary values (min, max, zero, empty, null)
• Edge cases and corner cases
• State transitions and side effects

3. Write Tests

Use project's testing framework:

• JavaScript/TypeScript: Jest, Vitest, Mocha
• Python: pytest, unittest
• Go: testing, testify
• Rust: built-in test framework

Target scenarios:

• Error handling and exceptions
• Boundary conditions
• Null/undefined/empty inputs
• Concurrent/async edge cases

4. Verify Improvement

Run coverage again and confirm measurable increase. Report:

• Before/after coverage percentages
• Number of new test cases added
• Files with the biggest coverage gains

Error Handling

No test framework detected

Solution: Check package.json, pyproject.toml, Cargo.toml, or go.mod for test dependencies. If none found, ask the user which framework to use and install it.

Coverage tool not installed

Solution: Install the appropriate coverage tool (nyc, pytest-cov, etc.) and retry.

Existing tests failing

Solution: Do not add new tests until existing failures are resolved. Report failing tests to the user first.

Guidelines

• Follow existing test patterns and naming conventions
• Place test files alongside source or in the project's existing test directory
• Group related test cases logically
• Use descriptive test names that explain the scenario
• Do not mock what you do not own — prefer integration tests for external boundaries