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