Test Suite Generator Skill

Test Suite Generator

Generate comprehensive test suites with coverage gap analysis and parallel test writing, following testing best practices across any project type and framework.

Target

$ARGUMENTS

Anti-Hallucination Guidelines

CRITICAL: Test generation must be based on ACTUAL code and VERIFIED project patterns:

Read source code first - Never write tests for code that has not been read and understood
Discover test framework - Do NOT assume pytest, vitest, jest, or any specific framework
Follow existing patterns - Match the project's existing test style, fixtures, and conventions exactly
Verify tests run - All generated tests must actually pass when executed
No invented APIs - Only test methods, functions, and interfaces that actually exist in the code
Real assertions - Every test must have meaningful assertions, not just "does not throw"
Coverage-driven - Focus on untested code paths, not duplicating existing coverage

Quality Gates

This skill includes automatic verification before completion:

Test Verification (Stop Hook)

When attempting to stop working, an automated verification agent runs to ensure quality:

Verification Steps:

Test Execution: Runs discovered test command. All tests (new and existing) must pass.
Coverage Check: If coverage tooling exists, verifies improvement over baseline.
Lint Check: Ensures test files pass linting rules.

Behavior:

All checks pass: Test generation marked complete
Any check fails: Completion blocked, error details provided, Claude continues fixing
Commands not found: Hook discovers them from CLAUDE.md or project files

Example blocked completion:

Test verification failed:

Tests: FAILED (2 new tests failing)
  - test_user_service_create: AttributeError: 'UserService' has no method 'create_user'
  - test_parse_config_empty: Expected ValueError, got None

Coverage: IMPROVED (72% → 78%)
Lint: PASSED

Cannot complete until all tests pass. Fix the failing tests.

Task Management

This skill uses Claude Code's Task Management System to track test generation progress with dependency-aware task tracking.

When to Use Tasks:

Generating tests for multiple files or modules
Coverage improvement across a codebase
Complex test generation requiring parallel subagents

When to Skip Tasks:

Adding 1-2 tests to a single file
Simple unit test additions
Quick test fixes

Implementation Workflow

Phase 0: Project Discovery (REQUIRED)

Step 0.1: Create Task Structure

Before generating tests, create the dependency-aware task structure:

TaskCreate:
  subject: "Phase 0: Discover project test workflow"
  description: "Identify test framework, coverage tools, and conventions"
  activeForm: "Discovering test workflow"

TaskCreate:
  subject: "Phase 1: Analyze coverage gaps"
  description: "Run coverage, identify untested code, prioritize targets"
  activeForm: "Analyzing coverage gaps"

TaskCreate:
  subject: "Phase 2: Create test plan"
  description: "Present test plan to user for approval"
  activeForm: "Creating test plan"

TaskCreate:
  subject: "Phase 3: Generate tests in parallel"
  description: "Spawn subagents to write tests for each module group"
  activeForm: "Generating tests"

TaskCreate:
  subject: "Phase 4: Quality verification"
  description: "Run all tests, check coverage improvement, lint"
  activeForm: "Verifying test quality"

TaskCreate:
  subject: "Phase 5: Final commit"
  description: "Commit tests with coverage summary"
  activeForm: "Committing tests"

# Set up strict sequential chain
TaskUpdate: { taskId: "2", addBlockedBy: ["1"] }
TaskUpdate: { taskId: "3", addBlockedBy: ["2"] }
TaskUpdate: { taskId: "4", addBlockedBy: ["3"] }
TaskUpdate: { taskId: "5", addBlockedBy: ["4"] }
TaskUpdate: { taskId: "6", addBlockedBy: ["5"] }

# Start first task
TaskUpdate: { taskId: "1", status: "in_progress" }

Step 0.2: Discover Test Workflow

Use Haiku-powered Explore agent for token-efficient discovery:

Use Task tool with Explore agent:
- prompt: "Discover the testing workflow for this project:
    1. Read CLAUDE.md if it exists - extract testing conventions and commands
    2. Check for task runners: Makefile, justfile, package.json scripts, pyproject.toml scripts
    3. Identify the test framework:
       - Python: pytest, unittest, nose2
       - JavaScript/TypeScript: vitest, jest, mocha, playwright, cypress
       - Other: go test, cargo test, etc.
    4. Identify the test command (e.g., make test, npm test, pytest, bun test)
    5. Identify the coverage command (e.g., pytest --cov, vitest --coverage, jest --coverage, make coverage)
    6. Identify the lint command
    7. Find existing test directory structure and naming conventions
    8. Look at 2-3 existing test files to understand:
       - Import patterns and test utilities
       - Fixture/mock patterns used
       - Assertion style (assert, expect, etc.)
       - Test organization (describe/it vs test functions)
       - Setup/teardown patterns
       - Factory or fixture patterns
    9. Check for test configuration files:
       - pytest.ini, conftest.py, setup.cfg [tool.pytest]
       - vitest.config.ts, jest.config.js
       - .nycrc, c8 config, istanbul config
    10. Note any test-related CI/CD configuration
    Return a structured summary of all testing infrastructure."
- subagent_type: "Explore"
- model: "haiku"

Store discovered commands and patterns for use in later phases.

Step 0.3: Complete Phase 0

TaskUpdate: { taskId: "1", status: "completed" }
TaskList  # Check that Task 2 is now unblocked

Phase 1: Coverage Gap Analysis

Goal: Identify what code lacks test coverage and prioritize test generation targets.

Step 1.1: Start Phase 1

TaskUpdate: { taskId: "2", status: "in_progress" }

Step 1.2: Establish Coverage Baseline

Run the discovered coverage command to get the current state:

# Examples (use the ACTUAL discovered command):
pytest --cov --cov-report=term-missing
vitest --coverage
jest --coverage
make coverage

Capture the output. If no coverage tooling exists, use an Explore agent to manually identify untested code:

Use Task tool with Explore agent:
- prompt: "Analyze test coverage gaps for this project:
    1. List all source files/modules in the project (exclude test files, configs, migrations)
    2. List all test files
    3. For each source file, check if a corresponding test file exists
    4. For files with tests, skim the test file to estimate which functions/methods are tested
    5. Identify files with no tests at all
    6. Identify complex files (many functions, classes, branching logic) that likely need more tests
    Return a structured report:
    - Files with NO test coverage (highest priority)
    - Files with PARTIAL coverage (functions/methods missing tests)
    - Files with GOOD coverage (low priority)
    - Overall estimated coverage percentage"
- subagent_type: "Explore"
- model: "haiku"

Step 1.3: Prioritize Test Targets

Rank files/modules for test generation by:

Critical business logic - Authentication, payments, data processing
Untested code - Files with zero test coverage
Complex code - High cyclomatic complexity, many branches
Recently changed - Code modified in recent commits (use git log --oneline -20 --name-only)
Error-prone areas - Code with known bugs or frequent changes

If the user specified target files/modules, prioritize those. Otherwise, use the ranking above.

Step 1.4: Complete Phase 1

TaskUpdate: { taskId: "2", status: "completed" }
TaskList  # Check that Task 3 is now unblocked

Phase 2: Test Plan (User Approval)

Goal: Present a test plan for user review before generating tests.

Step 2.1: Start Phase 2

TaskUpdate: { taskId: "3", status: "in_progress" }

Step 2.2: Present Test Plan

Use AskUserQuestion to present the plan and get approval:

AskUserQuestion:
  question: "Here's the test generation plan based on coverage analysis. Which approach do you prefer?"
  header: "Test Plan"
  options:
    - label: "Full coverage (Recommended)"
      description: "Generate tests for all [N] identified gaps: [list of modules]. Estimated [M] test files."
    - label: "Critical paths only"
      description: "Focus on [top modules] with highest business impact. Estimated [K] test files."
    - label: "Specific modules"
      description: "Let me specify which modules to test."

The plan should include for each target:

File/module path being tested
Functions/methods to cover
Test types: Unit tests, integration tests, edge cases
Estimated test count per file
Test file location following project conventions

Step 2.3: Complete Phase 2

TaskUpdate: { taskId: "3", status: "completed" }
TaskList  # Check that Task 4 is now unblocked

Phase 3: Parallel Test Generation

Goal: Generate tests efficiently using parallel subagents, one per module or file group.

Step 3.1: Start Phase 3

TaskUpdate: { taskId: "4", status: "in_progress" }

Step 3.2: Create Parallel Subagent Tasks

Group approved test targets into logical units (by module, feature area, or related files) and create a child task for each:

# Example: 3 module groups to test in parallel
TaskCreate:
  subject: "Write tests for auth module"
  description: "Generate unit tests for src/auth/ (login, register, token management)"
  activeForm: "Writing auth module tests"
  metadata: { parent: "4", module: "auth" }

TaskCreate:
  subject: "Write tests for user service"
  description: "Generate unit tests for src/services/user.py (CRUD, validation)"
  activeForm: "Writing user service tests"
  metadata: { parent: "4", module: "user-service" }

TaskCreate:
  subject: "Write tests for API routes"
  description: "Generate integration tests for src/routes/ (endpoints, middleware)"
  activeForm: "Writing API route tests"
  metadata: { parent: "4", module: "api-routes" }

# Phase 5 (Verification) blocked by ALL parallel tasks
TaskUpdate: { taskId: "5", addBlockedBy: ["child-task-ids"] }

Step 3.3: Spawn Parallel Subagents

For each module group, spawn a Sonnet subagent using the Task tool:

Subagent Instructions Template:

Generate comprehensive tests for [MODULE/FILES].

IMPORTANT: Read these source files FIRST to understand the actual code:
[LIST OF SOURCE FILES TO READ]

Then read these existing test files for patterns to follow:
[LIST OF EXISTING TEST FILES]

Project testing conventions (discovered in Phase 0):
- Test framework: [FRAMEWORK]
- Test command: [COMMAND]
- Test file naming: [PATTERN e.g., test_*.py, *.test.ts, *.spec.js]
- Test directory: [PATH]
- Fixture patterns: [DESCRIBE]
- Mock patterns: [DESCRIBE]
- Assertion style: [DESCRIBE]

Requirements:
1. Follow the EXACT test patterns from existing test files
2. Use the same import patterns, fixtures, and assertion style
3. Test coverage targets:
   - All public functions and methods
   - Happy path (normal inputs and expected outputs)
   - Edge cases (empty inputs, boundary values, null/undefined)
   - Error paths (invalid inputs, exceptions, error handling)
   - Branch coverage (if/else, switch, ternary paths)
4. Use descriptive test names that explain WHAT is being tested and EXPECTED behavior
5. Keep tests independent - no shared mutable state between tests
6. Mock external dependencies (databases, APIs, file system) appropriately
7. Do NOT test private/internal implementation details
8. Do NOT add unnecessary comments - test names should be self-documenting

After writing tests:
1. Run the test command to verify ALL tests pass
2. Fix any failures before reporting completion
3. Report: files created, test count, what is covered

Do NOT commit - the main agent handles commits.

Model Selection:

Use Sonnet (default) for test generation (requires code understanding and writing)
Use Haiku only for pure exploration tasks (not applicable in Phase 3)

Parallelization Strategy:

Spawn all independent module subagents simultaneously
Each subagent writes tests for its assigned module group
Subagents run tests locally to verify before completion

Step 3.4: Review Subagent Output

After each subagent completes:

Review the generated test files
Verify the tests follow project conventions
Update the corresponding child task: TaskUpdate: { taskId: "child-id", status: "completed" }

Step 3.5: Complete Phase 3

# After all subagent tasks complete
TaskUpdate: { taskId: "4", status: "completed" }
TaskList  # Verify Phase 5 is now unblocked

Phase 4: Quality Verification

Goal: Verify all tests pass together, coverage improved, and no regressions.

Step 4.1: Start Phase 4

TaskUpdate: { taskId: "5", status: "in_progress" }

Step 4.2: Run Full Test Suite

Execute the discovered test command to run ALL tests (new and existing):

# Use the ACTUAL discovered command, e.g.:
make test
pytest
npm test
bun test

ALL tests must pass. If any test fails:

Identify whether the failure is in a new test or an existing test
If new test fails: Fix the test (wrong assumption about code behavior)
If existing test fails: The new test introduced a side effect — investigate and fix
Re-run until all tests pass

Step 4.3: Verify Coverage Improvement

Run the coverage command and compare against the Phase 1 baseline:

# Use the ACTUAL discovered coverage command, e.g.:
pytest --cov --cov-report=term-missing
vitest --coverage
jest --coverage
make coverage

Record:

Baseline coverage: [X]% (from Phase 1)
New coverage: [Y]%
Improvement: +[Y-X]%
Uncovered lines remaining: [summary of what still lacks coverage]

Step 4.4: Lint Test Files

Run the discovered lint command on test files:

# Use the ACTUAL discovered lint command
make lint
ruff check tests/
npm run lint

Fix any linting errors in the generated test files.

Step 4.5: Complete Phase 4

TaskUpdate: { taskId: "5", status: "completed" }
TaskList  # Check that Task 6 is now unblocked

Phase 5: Final Commit

Step 5.1: Start Phase 5

TaskUpdate: { taskId: "6", status: "in_progress" }

Step 5.2: Create Commit

If /cc-arsenal:git:commit skill is available, use it. Otherwise, create a conventional commit manually:

git add [test files created/modified]
git commit -m "test: add comprehensive tests for [modules]

- [N] test files, [M] test cases added
- Coverage: [X]% → [Y]% (+[diff]%)
- Covers: [brief list of modules/features tested]
- Frameworks: [test framework used]"

Step 5.3: Complete Phase 5 and Test Generation

TaskUpdate: { taskId: "6", status: "completed" }
TaskList  # Show final status - all tasks should be completed

Output Summary

Provide a summary including:

Tests generated: Number of test files and test cases
Coverage improvement: Baseline → new coverage percentage
Modules covered: List of modules/files that received new tests
Test types: Unit, integration, edge cases breakdown
Remaining gaps: What still lacks coverage and recommendations
Commit: Reference to the commit created

Test Quality Principles

Generated tests must follow these principles:

Arrange-Act-Assert: Clear structure in every test
Single responsibility: Each test verifies one behavior
Descriptive names: Test name explains the scenario and expected outcome
Independence: Tests do not depend on execution order or shared state
Deterministic: Same result every time, no flaky tests
Fast: Unit tests run quickly; minimize I/O and external calls
Readable: Tests serve as documentation for the code under test
Maintainable: Avoid testing implementation details; test behavior and contracts

Additional Resources

For framework-specific test patterns, fixtures, and examples, see:

references/framework-patterns.md - Patterns for pytest, vitest, jest, Go, Rust, and more

Important Notes

Always run Phase 0 first - Never assume which test framework is available
Follow existing patterns - Match the project's test style exactly
Coverage is a guide, not a goal - Meaningful tests matter more than 100% coverage
No regressions - All existing tests must continue to pass
Ask when unsure - Use AskUserQuestion to clarify test scope or approach
Commit strategy - Prefer one clean commit with all tests over many small commits

Agent Skills: Test Suite Generator

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Skill Files