test-generator

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2 scripts

Generate or update tests for changed files in the current git branch, using statement coverage as the evaluation metric (target: 80%+). Use when: (1) the user asks to "write tests for my changes", "add tests for the current branch", or "improve coverage", (2) after implementing a feature to ensure adequate test coverage, (3) before a PR to verify changed code is tested. Supports Vitest and Cargo projects. Invoked with /test-generator or phrases like "generate tests", "test my changes", "cover the diff".

1installs

Sourcenimiusrd/agent-skills

Added on2026-02-19

NPX Install

npx skill4agent add nimiusrd/agent-skills test-generator

SKILL.md Content

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Test Generator

Automatically create or update tests for files changed in the current branch, iterating until statement coverage reaches the target threshold (default 80%).

Workflow

Detect changed files — run
```
scripts/detect-changes.sh [base-branch]
```
Discover project conventions — read existing tests, test config, and setup files
Write / update tests — for each uncovered file, create or extend its test file

Run coverage check — run

scripts/check-coverage.sh <threshold> [files...]

Iterate — if any file is below threshold, read the coverage report, add missing tests, repeat from step 4 (max 3 iterations)
Report — summarize final per-file coverage to the user

Step 1 — Detect Changed Files

bash

bash <skill-path>/scripts/detect-changes.sh main

Pass the base branch as argument (defaults to upstream or
```
main
```
).
Output: one source file path per line.
Filters out: test files, config, styles, assets, lock files,
```
__mocks__/
```
,
```
test/setup
```
.

If no files are output, inform the user there are no testable changes.

Step 2 — Discover Project Conventions

Before writing any test, read these to match existing style:

Test config —
```
vitest.config.*
```
,
```
vite.config.*
```
(test section),
```
Cargo.toml
```
Test setup — files referenced by
```
setupFiles
```
in config

Existing test for the file —

<name>.test.ts

,

<name>.spec.ts

, or

__tests__/<name>.ts

Neighboring tests — 1-2 test files in the same directory for style reference

Project rules —

AGENTS.md

,

CLAUDE.md

,

.eslintrc*

,

eslint.config.*

Key things to extract:

Test framework and assertion style (e.g.
```
expect()
```
,
```
assert
```
)
Import conventions (
```
import { describe } from 'vitest'
```
vs globals)
Mock patterns (manual mocks,
```
vi.mock()
```
)
File naming:
```
*.test.ts
```
vs
```
*.spec.ts
```
Any JSDoc / lint requirements on test files

Step 3 — Write / Update Tests

For each changed file without sufficient coverage:

If no test file exists → create one following the project naming convention.

If a test file exists → add new test cases; do not rewrite existing passing tests.

Test quality guidelines

Test behavior, not implementation details.
Cover: happy path, edge cases, error paths, boundary values.
Use descriptive
```
describe
```
/
```
it
```
block names that explain the expected behavior.

For React components: prefer

@testing-library/react

queries (

getByRole

,

getByText

) over

querySelector

.

For functions: test return values and side effects, not internal calls.
Mock external dependencies (API, file system, DB) but not the unit under test.
If the project uses
```
fast-check
```
, consider property tests for pure utility functions (name:
```
*.property.test.ts
```
).

Step 4 — Run Coverage Check

bash

bash <skill-path>/scripts/check-coverage.sh 80 src/services/foo.ts src/utils/bar.ts

First argument: threshold percentage.
Remaining arguments: filter output to only these files.

Output lines:

PASS 92.3% src/services/foo.ts

or

FAIL 65.0% src/utils/bar.ts

.

If the script fails to find coverage output, check that the coverage provider is installed (

@vitest/coverage-v8

,

@vitest/coverage-istanbul

, etc.) and install if missing.

Step 5 — Iterate

For each

FAIL

file:

Read the coverage JSON (
```
coverage/coverage-final.json
```
for vitest) to identify uncovered statements.
Add targeted test cases for uncovered branches/statements.
Re-run coverage check.
Repeat up to 3 iterations total. If still below threshold after 3 iterations, report remaining gaps to the user with suggestions.

Step 6 — Report

Summarize results:

## Test Coverage Report

| File | Coverage | Status |
|------|----------|--------|
| src/services/foo.ts | 92.3% | PASS |
| src/utils/bar.ts | 81.0% | PASS |
| src/components/Baz.tsx | 73.5% | FAIL |

Target: 80% | Passed: 2/3

For FAIL files, briefly explain what remains uncovered and suggest next steps.

Scripts

scripts/detect-changes.sh [base-branch]
— list changed source files needing tests
scripts/check-coverage.sh <threshold> [files...]
— run tests with coverage and report per-file results