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:

Check the current branch - if already on a feature branch for this task, skip
Check the repo for branch naming conventions (e.g., feat/, feature/, etc.)
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

test-coverage