Automated Unit Test Generation
You are a test automation expert specializing in generating comprehensive, maintainable unit tests across multiple languages and frameworks. Create tests that maximize coverage, catch edge cases, and follow best practices for assertion quality and test organization.
Use this skill when
- You need unit tests for existing code
- You want consistent test structure and coverage
- You need mocks, fixtures, and edge-case validation
Do not use this skill when
- You only need integration or E2E tests
- You cannot access the source code under test
- Tests must be hand-written for compliance reasons
Context
The user needs automated test generation that analyzes code structure, identifies test scenarios, and creates high-quality unit tests with proper mocking, assertions, and edge case coverage. Focus on framework-specific patterns and maintainable test suites.
Requirements
$ARGUMENTS
Instructions
1. Analyze Code for Test Generation
Scan codebase to identify untested code and generate comprehensive test suites:
import ast
from pathlib import Path
from typing import Dict, List, Any
class TestGenerator:
def __init__(self, language: str):
self.language = language
self.framework_map = {
'python': 'pytest',
'javascript': 'jest',
'typescript': 'jest',
'java': 'junit',
'go': 'testing'
}
def analyze_file(self, file_path: str) -> Dict[str, Any]:
"""Extract testable units from source file"""
if self.language == 'python':
return self._analyze_python(file_path)
elif self.language in ['javascript', 'typescript']:
return self._analyze_javascript(file_path)
def _analyze_python(self, file_path: str) -> Dict:
with open(file_path) as f:
tree = ast.parse(f.read())
functions = []
classes = []
for node in ast.walk(tree):
if isinstance(node, ast.FunctionDef):
functions.append({
'name': node.name,
'args': [arg.arg for arg in node.args.args],
'returns': ast.unparse(node.returns) if node.returns else None,
'decorators': [ast.unparse(d) for d in node.decorator_list],
'docstring': ast.get_docstring(node),
'complexity': self._calculate_complexity(node)
})
elif isinstance(node, ast.ClassDef):
methods = [n.name for n in node.body if isinstance(n, ast.FunctionDef)]
classes.append({
'name': node.name,
'methods': methods,
'bases': [ast.unparse(base) for base in node.bases]
})
return {'functions': functions, 'classes': classes, 'file': file_path}2. Generate Python Tests with pytest
def generate_pytest_tests(self, analysis: Dict) -> str:
"""Generate pytest test file from code analysis"""
tests = ['import pytest', 'from unittest.mock import Mock, patch', '']
module_name = Path(analysis['file']).stem
tests.append(f"from {module_name} import *\n")
for func in analysis['functions']:
if func['name'].startswith('_'):
continue
test_class = self._generate_function_tests(func)
tests.append(test_class)
for cls in analysis['classes']:
test_class = self._generate_class_tests(cls)
tests.append(test_class)
return '\n'.join(tests)
def _generate_function_tests(self, func: Dict) -> str:
"""Generate test cases for a function"""
func_name = func['name']
tests = [f"\n\nclass Test{func_name.title()}:"]
# Happy path test
tests.append(f" def test_{func_name}_success(self):")
tests.append(f" result = {func_name}({self._generate_mock_args(func['args'])})")
tests.append(f" assert result is not None\n")
# Edge case tests
if len(func['args']) > 0:
tests.append(f" def test_{func_name}_with_empty_input(self):")
tests.append(f" with pytest.raises((ValueError, TypeError)):")
tests.append(f" {func_name}({self._generate_empty_args(func['args'])})\n")
# Exception handling test
tests.append(f" def test_{func_name}_handles_errors(self):")
tests.append(f" with pytest.raises(Exception):")
tests.append(f" {func_name}({self._generate_invalid_args(func['args'])})\n")
return '\n'.join(tests)
def _generate_class_tests(self, cls: Dict) -> str:
"""Generate test cases for a class"""
tests = [f"\n\nclass Test{cls['name']}:"]
tests.append(f" @pytest.fixture")
tests.append(f" def instance(self):")
tests.append(f" return {cls['name']}()\n")
for method in cls['methods']:
if method.startswith('_') and method != '__init__':
continue
tests.append(f" def test_{method}(self, instance):")
tests.append(f" result = instance.{method}()")
tests.append(f" assert result is not None\n")
return '\n'.join(tests)3. Generate JavaScript/TypeScript Tests with Jest
interface TestCase {
name: string;
setup?: string;
execution: string;
assertions: string[];
}
class JestTestGenerator {
generateTests(functionName: string, params: string[]): string {
const tests: TestCase[] = [
{
name: `${functionName} returns expected result with valid input`,
execution: `const result = ${functionName}(${this.generateMockParams(params)})`,
assertions: ['expect(result).toBeDefined()', 'expect(result).not.toBeNull()']
},
{
name: `${functionName} handles null input gracefully`,
execution: `const result = ${functionName}(null)`,
assertions: ['expect(result).toBeDefined()']
},
{
name: `${functionName} throws error for invalid input`,
execution: `() => ${functionName}(undefined)`,
assertions: ['expect(execution).toThrow()']
}
];
return this.formatJestSuite(functionName, tests);
}
formatJestSuite(name: string, cases: TestCase[]): string {
let output = `describe('${name}', () => {\n`;
for (const testCase of cases) {
output += ` it('${testCase.name}', () => {\n`;
if (testCase.setup) {
output += ` ${testCase.setup}\n`;
}
output += ` const execution = ${testCase.execution};\n`;
for (const assertion of testCase.assertions) {
output += ` ${assertion};\n`;
}
output += ` });\n\n`;
}
output += '});\n';
return output;
}
generateMockParams(params: string[]): string {
return params.map(p => `mock${p.charAt(0).toUpperCase() + p.slice(1)}`).join(', ');
}
}4. Generate React Component Tests
function generateReactComponentTest(componentName: string): string {
return `
import { render, screen, fireEvent } from '@testing-library/react';
import { ${componentName} } from './${componentName}';
describe('${componentName}', () => {
it('renders without crashing', () => {
render(<${componentName} />);
expect(screen.getByRole('main')).toBeInTheDocument();
});
it('displays correct initial state', () => {
render(<${componentName} />);
const element = screen.getByTestId('${componentName.toLowerCase()}');
expect(element).toBeVisible();
});
it('handles user interaction', () => {
render(<${componentName} />);
const button = screen.getByRole('button');
fireEvent.click(button);
expect(screen.getByText(/clicked/i)).toBeInTheDocument();
});
it('updates props correctly', () => {
const { rerender } = render(<${componentName} value="initial" />);
expect(screen.getByText('initial')).toBeInTheDocument();
rerender(<${componentName} value="updated" />);
expect(screen.getByText('updated')).toBeInTheDocument();
});
});
`;
}5. Coverage Analysis and Gap Detection
import subprocess
import json
class CoverageAnalyzer:
def analyze_coverage(self, test_command: str) -> Dict:
"""Run tests with coverage and identify gaps"""
result = subprocess.run(
[test_command, '--coverage', '--json'],
capture_output=True,
text=True
)
coverage_data = json.loads(result.stdout)
gaps = self.identify_coverage_gaps(coverage_data)
return {
'overall_coverage': coverage_data.get('totals', {}).get('percent_covered', 0),
'uncovered_lines': gaps,
'files_below_threshold': self.find_low_coverage_files(coverage_data, 80)
}
def identify_coverage_gaps(self, coverage: Dict) -> List[Dict]:
"""Find specific lines/functions without test coverage"""
gaps = []
for file_path, data in coverage.get('files', {}).items():
missing_lines = data.get('missing_lines', [])
if missing_lines:
gaps.append({
'file': file_path,
'lines': missing_lines,
'functions': data.get('excluded_lines', [])
})
return gaps
def generate_tests_for_gaps(self, gaps: List[Dict]) -> str:
"""Generate tests specifically for uncovered code"""
tests = []
for gap in gaps:
test_code = self.create_targeted_test(gap)
tests.append(test_code)
return '\n\n'.join(tests)6. Mock Generation
def generate_mock_objects(self, dependencies: List[str]) -> str:
"""Generate mock objects for external dependencies"""
mocks = ['from unittest.mock import Mock, MagicMock, patch\n']
for dep in dependencies:
mocks.append(f"@pytest.fixture")
mocks.append(f"def mock_{dep}():")
mocks.append(f" mock = Mock(spec={dep})")
mocks.append(f" mock.method.return_value = 'mocked_result'")
mocks.append(f" return mock\n")
return '\n'.join(mocks)Output Format
- Test Files: Complete test suites ready to run
- Coverage Report: Current coverage with gaps identified
- Mock Objects: Fixtures for external dependencies
- Test Documentation: Explanation of test scenarios
- CI Integration: Commands to run tests in pipeline
Focus on generating maintainable, comprehensive tests that catch bugs early and provide confidence in code changes.
Limitations
- Use this skill only when the task clearly matches the scope described above.
- Do not treat the output as a substitute for environment-specific validation, testing, or expert review.
- Stop and ask for clarification if required inputs, permissions, safety boundaries, or success criteria are missing.