TestGen Skill - AI Test Generation

Generate comprehensive tests with automatic framework detection, expert agent routing, and project convention matching.

Architecture

testgen <target> [--type] [--focus] [--depth]
    │
    ├─→ Step 1: Analyze Target
    │     ├─ File exists? → Read and parse
    │     ├─ Function specified? → Extract signature
    │     ├─ Directory? → List source files
    │     └─ Find existing tests (avoid duplicates)
    │
    ├─→ Step 2: Detect Framework (parallel)
    │     ├─ package.json → jest/vitest/mocha/cypress/playwright
    │     ├─ pyproject.toml → pytest/unittest
    │     ├─ go.mod → go test
    │     ├─ Cargo.toml → cargo test
    │     ├─ composer.json → phpunit/pest
    │     └─ Check existing test patterns
    │
    ├─→ Step 3: Load Project Standards
    │     ├─ AGENTS.md, CLAUDE.md conventions
    │     ├─ Existing test file structure
    │     └─ Naming conventions (*.test.ts vs *.spec.ts)
    │
    ├─→ Step 4: Route to Expert Agent
    │     ├─ .ts → typescript-expert
    │     ├─ .tsx/.jsx → react-expert
    │     ├─ .vue → vue-expert
    │     ├─ .py → python-expert
    │     ├─ .go → go-expert
    │     ├─ .rs → rust-expert
    │     ├─ .php → laravel-expert
    │     ├─ E2E/Cypress → cypress-expert
    │     ├─ Playwright → typescript-expert
    │     ├─ --visual → Chrome DevTools MCP
    │     └─ Multi-file → parallel expert dispatch
    │
    ├─→ Step 5: Generate Tests
    │     ├─ Create test file in correct location
    │     ├─ Follow detected conventions
    │     └─ Include: happy path, edge cases, error handling
    │
    └─→ Step 6: Integration
          ├─ Auto-create task (TaskCreate) for verification
          └─ Suggest: run tests, /review, /save

Execution Steps

Step 1: Analyze Target

# Check if target exists
test -f "$TARGET" && echo "FILE" || test -d "$TARGET" && echo "DIRECTORY"

# For function-specific: extract signature
command -v ast-grep >/dev/null 2>&1 && ast-grep -p "function $FUNCTION_NAME" "$FILE"

# Fallback to ripgrep
rg "(?:function|const|def|public|private)\s+$FUNCTION_NAME" "$FILE" -A 10

Check for existing tests:

fd -e test.ts -e spec.ts -e test.js -e spec.js | rg "$BASENAME"
fd "test_*.py" | rg "$BASENAME"

Step 2: Detect Framework

JavaScript/TypeScript:

cat package.json 2>/dev/null | jq -r '.devDependencies | keys[]' | grep -E 'jest|vitest|mocha|cypress|playwright|@testing-library'

Python:

grep -E "pytest|unittest|nose" pyproject.toml setup.py requirements*.txt 2>/dev/null

Go:

test -f go.mod && echo "go test available"

Rust:

test -f Cargo.toml && echo "cargo test available"

PHP:

cat composer.json 2>/dev/null | jq -r '.["require-dev"] | keys[]' | grep -E 'phpunit|pest|codeception'

Step 3: Load Project Standards

# Claude Code conventions
cat AGENTS.md 2>/dev/null | head -50
cat CLAUDE.md 2>/dev/null | head -50

# Test config files
cat jest.config.* vitest.config.* pytest.ini pyproject.toml 2>/dev/null | head -30

Test location conventions:

# JavaScript
src/utils/helper.ts → src/utils/__tests__/helper.test.ts  # __tests__ folder
                    → src/utils/helper.test.ts            # co-located
                    → tests/utils/helper.test.ts          # separate tests/

# Python
app/utils/helper.py → tests/test_helper.py               # tests/ folder
                    → tests/utils/test_helper.py         # mirror structure

# Go
pkg/auth/token.go → pkg/auth/token_test.go               # co-located (required)

# Rust
src/auth.rs → src/auth.rs (mod tests { ... })            # inline tests
            → tests/auth_test.rs                          # integration tests

Step 4: Route to Expert Agent

File Pattern	Primary Expert	Secondary
*.ts	typescript-expert	-
*.tsx, *.jsx	react-expert	typescript-expert
*.vue	vue-expert	typescript-expert
*.py	python-expert	-
*.go	go-expert	-
*.rs	rust-expert	-
*.php	laravel-expert	-
*.cy.ts, cypress/*	cypress-expert	-
*.spec.ts (Playwright)	typescript-expert	-
playwright/*, e2e/*	typescript-expert	-
*.sh, *.bash	bash-expert	-
(--visual flag)	Chrome DevTools MCP	typescript-expert

Invoke via Task tool:

Task tool with subagent_type: "[detected]-expert"
Prompt includes:
  - Source file content
  - Function signatures to test
  - Detected framework and conventions
  - Requested test type and focus

Step 5: Generate Tests

Test categories based on --focus:

Focus	What to Generate
happy	Normal input, expected output
edge	Boundary values, empty inputs, nulls
error	Invalid inputs, exceptions, error handling
all	All of the above (default)

Depth levels:

Depth	Coverage
quick	Happy path only, 1-2 tests per function
normal	Happy + common edge cases (default)
thorough	Comprehensive: all paths, mocking, async

Step 6: Integration

Auto-create task:

TaskCreate:
  subject: "Run generated tests for src/auth.ts"
  description: "Verify generated tests pass and review edge cases"
  activeForm: "Running generated tests for auth.ts"

Suggest next steps:

Tests generated: src/auth.test.ts

Next steps:
1. Run tests: npm test src/auth.test.ts
2. Review and refine edge cases
3. Use /save to persist tasks across sessions

---

Expert Routing Details

TypeScript/JavaScript → typescript-expert

• Proper type imports
• Generic type handling
• Async/await patterns
• Mock typing

React/JSX → react-expert

• React Testing Library patterns
• Component rendering tests
• Hook testing (renderHook)
• Accessibility queries (getByRole)

Vue → vue-expert

• Vue Test Utils patterns
• Composition API testing
• Pinia store mocking

Python → python-expert

• pytest fixtures
• Parametrized tests
• Mock/patch patterns
• Async test handling

Go → go-expert

• Table-driven tests ([]struct pattern)
• testing.T and subtests (t.Run)
• Testify assertions (when detected)
• Benchmark functions (testing.B)
• Parallel tests (t.Parallel())

Rust → rust-expert

• #[test] attribute functions
• #[cfg(test)] module organization
• #[should_panic] for error testing
• proptest/quickcheck for property testing

PHP/Laravel → laravel-expert

• PHPUnit/Pest patterns
• Database transactions
• Factory usage

E2E → cypress-expert

• Page object patterns
• Custom commands
• Network stubbing

Playwright → typescript-expert

• Page object model patterns
• Locator strategies
• Visual regression testing

---

CLI Tool Integration

Tool	Purpose	Fallback
jq	Parse package.json	Read tool
rg	Find existing tests	Grep tool
ast-grep	Parse function signatures	ripgrep patterns
fd	Find test files	Glob tool
Chrome DevTools MCP	Visual testing (--visual)	Playwright/Cypress

Graceful degradation:

command -v jq >/dev/null 2>&1 && cat package.json | jq '.devDependencies' || cat package.json

---

Reference Files

For framework-specific code examples, see:

• frameworks.md - Complete test examples for all supported languages
• visual-testing.md - Chrome DevTools integration for --visual flag

---

Integration

Command	Relationship
/review	Review generated tests before committing
/explain	Understand complex code before testing
/save	Track test coverage goals