designing-tests

describe("[Unit] ComponentName", () => {
  describe("methodName", () => {
    it("should [expected behavior] when [condition]", () => {
      // Arrange
      const input = createTestInput();
 
      // Act
      const result = methodName(input);
 
      // Assert
      expect(result).toEqual(expectedOutput);
    });
 
    it("should throw error when [invalid condition]", () => {
      expect(() => methodName(invalidInput)).toThrow(ExpectedError);
    });
  });
});

describe("[Integration] API /users", () => {
  beforeAll(async () => {
    await setupTestDatabase();
  });
 
  afterAll(async () => {
    await teardownTestDatabase();
  });
 
  it("should create user and return 201", async () => {
    const response = await request(app)
      .post("/users")
      .send({ name: "Test", email: "test@example.com" });
 
    expect(response.status).toBe(201);
    expect(response.body.id).toBeDefined();
  });
});

import { test, expect } from "@playwright/test";
 
test.describe("[E2E] User Registration Flow", () => {
  test("should complete registration successfully", async ({ page }) => {
    await page.goto("/register");
 
    await page.getByTestId("email").fill("new@example.com");
    await page.getByTestId("password").fill("SecurePass123!");
    await page.getByTestId("submit").click();
 
    await expect(page.locator(".welcome-message")).toBeVisible();
    await expect(page).toHaveURL("/dashboard");
  });
});

{
  "coverageThreshold": {
    "global": {
      "branches": 80,
      "functions": 80,
      "lines": 80,
      "statements": 80
    },
    "src/core/": {
      "branches": 95,
      "functions": 95
    }
  }
}

// factories/user.js
export const userFactory = (overrides = {}) => ({
  id: faker.string.uuid(),
  name: faker.person.fullName(),
  email: faker.internet.email(),
  createdAt: new Date(),
  ...overrides,
});
 
// Usage
const admin = userFactory({ role: "admin" });

// fixtures/users.json
{
  "validUser": { "name": "Test", "email": "test@example.com" },
  "invalidUser": { "name": "", "email": "invalid" }
}

// API mocking with MSW
import { http, HttpResponse } from "msw";
 
export const handlers = [
  http.get("/api/users", () => {
    return HttpResponse.json([{ id: 1, name: "John" }]);
  }),
];
 
// Time mocking
vi.useFakeTimers();
vi.setSystemTime(new Date("2024-01-01"));

Test Validation:
- [ ] All tests pass: `npm test`
- [ ] Coverage meets thresholds: `npm test -- --coverage`
- [ ] No flaky tests (run multiple times)
- [ ] Tests are independent (order doesn't matter)
- [ ] Test names clearly describe behavior

# Run tests
npm test
 
# Run with coverage
npm test -- --coverage
 
# Run specific test file
npm test -- path/to/test.spec.ts
 
# Run in watch mode during development
npm test -- --watch