Test Expert

Test Expert

This skill helps you generate robust, idiomatic test code and ensure it is placed in the correct project location following industry best practices.

Workflow

1. Detect Environment: Identify language and framework (check pyproject.toml, package.json, go.mod).
2. Determine Location:
   • Python: tests/ (root level) or src/package/tests/.
   • JS/TS: src/__tests__/ or *.test.ts collocated.
   • Go: *_test.go collocated.
   • Java/Kotlin: src/test/java/.
3. Generate Test Case:
   • AAA Pattern: Arrange, Act, Assert.
   • Descriptive Names: test_should_return_404_when_user_not_found.
   • Isolation: Mock external I/O (DB, Network).
4. Verify: Run the tests to prove they fail (RED) and then pass (GREEN).

Deep Dive: Python (pytest)

Use pytest as the default unless strictly constrained to unittest.

1. The Basics

def test_add_should_sum_two_numbers():
    # Arrange
    a, b = 2, 3
    # Act
    result = add(a, b)
    # Assert
    assert result == 5  # No self.assertEqual needed

2. Parametrization (Don't write loops)

import pytest

@pytest.mark.parametrize("input_a, input_b, expected", [
    (1, 1, 2),
    (10, 20, 30),
    (-1, 1, 0),
])
def test_add_various_cases(input_a, input_b, expected):
    assert add(input_a, input_b) == expected

3. Fixtures (Setup/Teardown)

Use fixtures for reusable state. Scope them appropriately (function, module, session).

@pytest.fixture
def sample_user():
    return User(name="Alice", age=30)

def test_user_age(sample_user):
    assert sample_user.age == 30

4. Mocking (External Dependencies)

Use unittest.mock (standard lib) or pytest-mock fixture.

from unittest.mock import Mock

def test_api_call(mocker): # using pytest-mock
    # Arrange
    mock_api = mocker.patch("my_app.services.api_client.get")
    mock_api.return_value = {"status": "ok"}
    
    # Act
    result = fetch_data()
    
    # Assert
    assert result == "ok"
    mock_api.assert_called_once()

Deep Dive: TypeScript (Vitest/Jest)

1. Async & Spies

import { vi, describe, it, expect } from 'vitest';
import { UserService } from './user-service';

describe('UserService', () => {
  it('should save user', async () => {
    // Arrange
    const dbMock = { save: vi.fn().mockResolvedValue(true) };
    const service = new UserService(dbMock);
    
    // Act
    await service.register('alice');
    
    // Assert
    expect(dbMock.save).toHaveBeenCalledWith('alice');
  });
});

Quality Gate Checklist

• Location: Is the file in the standard path?
• Imports: Are source modules imported correctly?
• Style: snake_case for Python tests, camelCase for JS/TS tests.
• Behavior: Does it test behavior, not implementation details?