Test Coverage

Test Coverage Expander

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

When to Use

• User asks to "increase test coverage", "add more tests", "expand unit tests", or "cover edge cases"
• A CI pipeline reports low coverage and the user wants it improved
• A code review flags untested error paths or boundary conditions
• The user wants to identify and fill gaps in an existing test suite before a release

Stack (detect before Step 1 of Workflow)

Detect the project's language from its manifest file and use the matching commands throughout the Workflow below:

If none of these manifests is found, see Edge Cases — "No test framework detected".

Repo Sync Before Edits (mandatory)

Before creating/updating/deleting files in an existing repository, sync the current branch with remote. First save git status --porcelain as the pre-sync list; Step 4 never stages those paths.

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. Run git rev-parse --abbrev-ref HEAD. If it prints a branch other than main or master that was created for this task, skip to Step 1.
2. Run git branch -a and note the prefix most existing branches use (e.g., feat/, feature/, test/).
3. Create and switch to a new branch with that prefix. If no prefix is in use, name it feat/test-coverage.

1. Analyze Coverage

Run the coverage command for the detected Stack above. Record the total coverage percentage and the pass/fail counts as the baseline. If any test fails, stop here (see Edge Cases).

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 the test framework for the detected Stack above.

Target scenarios:

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

4. Verify Improvement

1. Run the full test suite. If a new test fails, fix or remove it, then rerun. If a previously passing test now fails, report PARTIAL and name it.
2. Run the same coverage command as Step 1.
3. Compare the new total with the Step 1 baseline. If it is not strictly higher, report PARTIAL and list the Step 2 gaps that are still untested.
4. If the full suite passed in item 1, commit the new tests on the feature branch with a message that records the before/after coverage percentages and the files newly covered. Stage each test file this run wrote by explicit path (git add tests/test_parser.py); never git add -A, git add . or git commit -a, which would sweep in user work Repo Sync restored. Never stage a path on the pre-sync list. Stage a changed manifest or lockfile (Coverage tool not installed) only with its reason in the commit message. Check git diff --cached --name-only before committing. Under Uncertainty:, list each changed file left unstaged, or every new test file when the commit is skipped (failed suite or regression).
5. Print the final report. It opens with Result: — COMPLETE, PARTIAL — reason, or BLOCKED — reason — followed by:
   • Evidence: the commands that ran, with before/after totals and pass/fail counts
   • Uncertainty: what was not checked (e.g., excluded paths, CI not run, covered lines without output assertions)
   • Decision: the action that needs approval, or No approval needed, then any remaining user action (e.g., push the branch, open a PR)
   • The number of new test cases and the files with the biggest coverage gains

Expected Output

After a successful run on a Python project, the final verification report shows:

Result:       COMPLETE — coverage 61% → 84%, all tests pass
Evidence:     pytest --cov=. --cov-report=term-missing (before): 61% (47/77 statements), 47 passed
              same command (after): 84% (65/77 statements), 56 passed, 0 failed
Uncertainty:  CI not run; src/vendor/ excluded from coverage
Decision:     No approval needed. Next: push feat/test-coverage and open a PR.

New tests added: 9
Files improved:
  - src/parser.py        52% → 91%  (+7 tests: null input, empty string, unicode overflow)
  - src/auth.py          71% → 88%  (+2 tests: expired token, missing header)