mavka-ai/unit-tests-skills

Unit Test Skills by Mavka

Don’t just ask your AI agent to write tests. Give it a testing process.

These skills make your agent plan coverage first, generate focused Java unit tests, compile them, and run them before it reports done.

Plan → Generate → Compile → Run

Java · JUnit 5 · Mockito · AssertJ

~42% → ~83–92% mutation score · 100% branch coverage One pinned Spring Petclinic target · 12 injected defects · Claude Code 2.1.276 / OPUS-5 · Codex 0.155.1 / gpt-5.6-sol

Install the skills ↓

Why

An agent asked to “write tests” can stop as soon as the build is green. But a green suite with full branch coverage can still miss real defects: the benchmark below shows exactly that.

These skills give the agent a testing process instead of a one-shot prompt: plan the cases from the code’s branches, generate focused tests, compile them, and run them before reporting done. Use them when you:

• add unit tests to an untested Java service or controller;
• want to review the planned test cases before any test code is written;
• want generated tests that follow consistent naming and structure rules.

See the difference

Same green build. Same 100% branch coverage. More defects detected.

In one controlled benchmark, Claude and Codex each generated tests for the same pinned Spring Petclinic target, first without the skill and then with it. We ran all four suites against the original code and the same 12 deliberately introduced defects.

Engines: Claude Code 2.1.276 with OPUS-5 · Codex 0.155.1 with gpt-5.6-sol

All four suites built successfully and reported 100% branch coverage. Mutation testing revealed the difference: the suites generated with the skill detected 10–11 of the 12 injected defects instead of 5.

Benchmark scope: One fixed scenario on a pinned Spring Petclinic target. Results may vary across codebases, tasks, models, and runs.

Installation

Option 1: Using npx skills (Recommended)

For reliable automatic skill discovery, complete both steps:

1. Install the skills:

npx skills add mavka-ai/unit-tests-skills

2. Add the AGENTS.md snippet to your project’s AGENTS.md file so AI agents know when and how to use the installed skills.

Or install specific skills:

npx skills add mavka-ai/unit-tests-skills --skill generate-test-cases
npx skills add mavka-ai/unit-tests-skills --skill generate-tests

Option 2: Using openskills (Recommended for other agents)

openskills automatically generates AGENTS.md for maximum AI agent effectiveness.

# Install skills
npx openskills install mavka-ai/unit-tests-skills

# Auto-generate/update AGENTS.md with installed skills
npx openskills sync

Why openskills? According to Vercel’s research, skills alone trigger only 53% of the time. With AGENTS.md, success rate jumps to 100%.

Option 3: Claude Code plugin (Recommended for Claude Code)

/plugin marketplace add mavka-ai/unit-tests-skills
/plugin install unit-tests-skills@mavka

Skills are namespaced by the plugin, so they are invoked as /unit-tests-skills:generate-tests and /unit-tests-skills:generate-test-cases. See Updating and Uninstalling to keep the installed plugin current or remove it.

Try it

Examples below use the plain command form. If you installed as a plugin, prefix the skill name with the plugin: /unit-tests-skills:generate-tests.

Generate tests for a class:

/generate-tests src/services/OrderService.java

Only plan the test cases, without generating code:

/generate-test-cases src/services/OrderService.java

What you get

Test Cases

## Test Cases for OrderService.calculateTotal

### 1. calculateTotal_validProducts_returnsSum
- **Given:** List with products priced at 50.0 and 100.0
- **When:** calculateTotal() is called
- **Then:** Returns 150.0
- **Code branch:** Happy path

### 2. calculateTotal_emptyList_throwsIllegalArgumentException
- **Given:** Empty product list
- **When:** calculateTotal() is called
- **Then:** Throws IllegalArgumentException
- **Code branch:** Validation - empty input

Generated Test

@ExtendWith(MockitoExtension.class)
class OrderServiceTest {

    @Mock
    private ProductRepository productRepository;

    @InjectMocks
    private OrderService orderService;

    @Test
    void calculateTotal_validProducts_returnsSum() {
        // Given
        var product1 = new Product("A", 50.0);
        var product2 = new Product("B", 100.0);
        when(productRepository.findAll()).thenReturn(List.of(product1, product2));

        // When
        double actualTotal = orderService.calculateTotal();

        // Then
        double expectedTotal = 150.0;
        assertThat(actualTotal).isEqualTo(expectedTotal);
    }
}

How it works

/generate-tests runs the full workflow unattended:

1. Plan: analyzes the source code and prints a structured list of test cases
2. Generate: writes the test files from that plan
3. Compile: verifies the tests compile
4. Run: runs the tests and reports the result

Available skills

Claude Code namespaces plugin skills by plugin name, so the command depends on how you installed. Use the Plugin command after Option 3; use the plain Command after openskills or npx skills.

Testing Principles

These skills enforce proven testing practices:

General Rules (All Languages)

Supported agents

• Claude Code: install as a plugin (Option 3) or with npx skills.
• Codex and other agents that read AGENTS.md: install with npx skills or openskills, and make sure your AGENTS.md references the skills.

Why AGENTS.md Matters

AGENTS.md provides persistent context to AI agents on every turn, without requiring them to decide to load skills first. See the full article for details.

Supported languages

Java

• JUnit 5 + Mockito + AssertJ
• @ExtendWith(MockitoExtension.class) for unit tests
• FORBIDDEN: @SpringBootTest in unit tests
• Use ArgumentCaptor instead of any() for DTOs
• Explicit JSON literals (no objectMapper.writeValueAsString())
• OutputCaptureExtension for log verification

Updating and Uninstalling

Use the commands for the installation method you originally chose.

npx skills

Update both skills to their latest versions:

npx skills update generate-test-cases generate-tests

Remove both skills:

npx skills remove generate-test-cases generate-tests

Because the AGENTS.md snippet for this installation method is added manually, remove that snippet manually after uninstalling the skills.

openskills

Update installed skills from their recorded sources, then regenerate AGENTS.md:

npx openskills update
npx openskills sync

Remove both skills, then regenerate AGENTS.md so it no longer references them:

npx openskills remove generate-test-cases
npx openskills remove generate-tests
npx openskills sync

Claude Code plugin

Refresh the marketplace listing, then update the installed plugin:

/plugin marketplace update mavka
/plugin update unit-tests-skills@mavka

Remove the installed plugin:

/plugin uninstall unit-tests-skills@mavka

If you no longer use anything from the mavka marketplace, you can also remove the marketplace itself with /plugin marketplace remove mavka. Removing a marketplace also uninstalls plugins installed from it.

Documentation

• Google’s unit test best practices — source review and implementation status for the rules in this repository.
• The Complete Guide to Building Skills for Claude

Contributing

Contributions are welcome via Pull Requests. All PRs require review and approval from maintainers before merging.

When adding new rules:

1. Place general rules in skills/{skill-name}/rules/general/ (or rules/tests/general/ for generate-tests)
2. Place language-specific rules in skills/generate-tests/rules/tests/{language}/unit/
3. Update skill files if new rules need explicit reference
4. Ensure your changes follow the existing format and style

Project Structure

skills/
├── generate-test-cases/
│   ├── SKILL.md
│   └── rules/general/
└── generate-tests/
    ├── SKILL.md
    └── rules/tests/
        ├── general/
        ├── java/unit/
        └── post-generation/

Repository Protection

This repository uses branch protection rules:

• Direct pushes to main are disabled
• All changes require a Pull Request
• PRs require at least one approval from CODEOWNERS
• Status checks must pass before merging

License

Released under the MIT License — free to use, modify, and embed in commercial and closed-source projects, provided the copyright notice is retained.

Trademark

The MIT License covers copyright only. Mavka® is a registered European Union trade mark (EUTM No. 019310487) of CLEAR-SOLUTIONS sp. z o.o., which operates as Mavka AI; Mavka AI™ and the Mavka AI logo are used as unregistered marks. The marks are not licensed with the code. Referring to the project by name is fine; using them in your own product or fork’s name is not. See TRADEMARK.md for the full policy.

Built by Mavka AI

Unit Test Skills is built by Mavka AI, where we create the best AI tools and skills for developers. We’re a digital engineering company that helps growing tech businesses remove architectural debt, modernize systems, and put AI to work in everyday engineering.

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