test-generation

name	test-generation
description	TDD patterns and language-specific test examples for TypeScript/Jest, Python/pytest, and Go. Use when writing tests, increasing coverage, or implementing test-driven development.
license	MIT
compatibility	Claude Code, GitHub Copilot, OpenCode, Cursor, Codex, Gemini CLI
metadata	{"author":"paruff","suite":"uFawkesAI"}

Skill: Test Generation

Load trigger: "load test-generation skill" > DORA: Cap 5 (Small Batches / Shift Left on Quality) Token cost: Low

TDD Pattern — Language Agnostic

Commit Sequence (required order)

1. test: add failing tests for [feature]      ← CI fails here intentionally
2. feat: implement [feature] to pass tests
3. refactor: clean up [feature] if needed

TypeScript/Jest Pattern

// tests/services/auth.test.ts
import { signIn } from "../src/services/auth";
import { mockFirebaseAuth } from "./mocks/firebase";

describe("signIn", () => {
  it("returns user object on valid credentials", async () => {
    mockFirebaseAuth.mockResolvedValueOnce({
      uid: "user-123",
      email: "[e-mail]",
    });
    const result = await signIn("[e-mail]", "valid-password");
    expect(result.uid).toBe("user-123");
  });

  it("throws AuthError when credentials are invalid", async () => {
    mockFirebaseAuth.mockRejectedValueOnce(new Error("auth/wrong-password"));
    await expect(signIn("[e-mail]", "wrong")).rejects.toThrow("auth/wrong-password");
  });

  it("throws AuthError when email is malformed", async () => {
    await expect(signIn("not-an-email", "password")).rejects.toThrow();
  });
});

Python/pytest Pattern

# tests/test_auth.py
import pytest
from unittest.mock import patch, MagicMock
from src.services.auth import sign_in, AuthError

def test_sign_in_returns_user_on_valid_credentials():
    with patch('src.services.auth.firebase_auth') as mock_auth:
        mock_auth.sign_in_with_password.return_value = {'uid': 'user-123'}
        result = sign_in('[e-mail]', 'valid-password')
        assert result['uid'] == 'user-123'

def test_sign_in_raises_on_invalid_credentials():
    with patch('src.services.auth.firebase_auth') as mock_auth:
        mock_auth.sign_in_with_password.side_effect = Exception('INVALID_PASSWORD')
        with pytest.raises(AuthError):
            sign_in('[e-mail]', 'wrong')

Go Pattern

// services/auth_test.go
package services

import (
    "testing"
    "errors"
)

func TestSignIn_ValidCredentials_ReturnsUser(t *testing.T) {
    mockAuth := &MockAuthProvider{
        SignInFunc: func(email, password string) (*User, error) {
            return &User{UID: "user-123"}, nil
        },
    }
    svc := NewAuthService(mockAuth)
    user, err := svc.SignIn("[e-mail]", "valid-password")
    if err != nil { t.Fatalf("unexpected error: %v", err) }
    if user.UID != "user-123" { t.Errorf("expected user-123, got %s", user.UID) }
}

Coverage Gap Triage Order

1. Uncovered error paths (highest value — crashes and data loss live here)
2. Uncovered branch conditions (if/else, switch cases)
3. Uncovered integration boundaries (service calls, DB calls)
4. Happy path gaps (lowest marginal value if 1–3 are covered)

Mock Boundary Rule

Mock at the I/O boundary only:

• ✅ Mock HTTP client, database driver, filesystem, external SDK
• ❌ Mock internal service functions (tests implementation, not behavior)
• ❌ Mock the thing you are testing