testing-suite

name	testing-suite
description	Setup and configure testing infrastructure with Vitest, Playwright, and testing patterns. Use when users need to add tests, configure test runners, implement TDD workflows, or create E2E test suites. Covers unit, integration, and end-to-end testing strategies.

Testing Suite

Complete testing infrastructure for modern TypeScript/JavaScript applications.

Decision Tree

User request → What type of testing?
    │
    ├─ Unit Tests
    │   ├─ Runner?
    │   │   ├─ Vitest → Fast, Vite-native, ESM
    │   │   ├─ Jest → Mature, wide ecosystem
    │   │   └─ Bun test → Ultra-fast, built-in
    │   │
    │   └─ What to test?
    │       ├─ Functions → Pure logic, utilities
    │       ├─ Components → React Testing Library
    │       ├─ Hooks → @testing-library/react-hooks
    │       └─ API handlers → MSW for mocking
    │
    ├─ Integration Tests
    │   ├─ Database → Test containers, in-memory
    │   ├─ API → Supertest, actual endpoints
    │   └─ Services → Real dependencies
    │
    ├─ E2E Tests
    │   ├─ Playwright → Cross-browser, fast
    │   ├─ Cypress → Great DX, dashboard
    │   └─ What to test?
    │       ├─ User flows → Critical paths
    │       ├─ Visual regression → Screenshots
    │       └─ Accessibility → axe-core
    │
    └─ Test Strategy
        ├─ TDD → Red-green-refactor
        ├─ Coverage → Istanbul/c8
        └─ CI → GitHub Actions integration

Quick Start

Vitest Setup

# Install
pnpm add -D vitest @vitest/coverage-v8 @vitest/ui

# With React
pnpm add -D @testing-library/react @testing-library/jest-dom jsdom

// vitest.config.ts
import { defineConfig } from "vitest/config";
import react from "@vitejs/plugin-react";

export default defineConfig({
  plugins: [react()],
  test: {
    globals: true,
    environment: "jsdom",
    setupFiles: ["./src/test/setup.ts"],
    include: ["src/**/*.{test,spec}.{ts,tsx}"],
    coverage: {
      provider: "v8",
      reporter: ["text", "json", "html"],
      exclude: ["node_modules/", "src/test/"],
    },
  },
});

Playwright Setup

# Install
pnpm add -D @playwright/test
npx playwright install

// playwright.config.ts
import { defineConfig, devices } from "@playwright/test";

export default defineConfig({
  testDir: "./e2e",
  fullyParallel: true,
  forbidOnly: !!process.env.CI,
  retries: process.env.CI ? 2 : 0,
  workers: process.env.CI ? 1 : undefined,
  reporter: "html",
  use: {
    baseURL: "http://localhost:3000",
    trace: "on-first-retry",
    screenshot: "only-on-failure",
  },
  projects: [
    { name: "chromium", use: { ...devices["Desktop Chrome"] } },
    { name: "firefox", use: { ...devices["Desktop Firefox"] } },
    { name: "webkit", use: { ...devices["Desktop Safari"] } },
  ],
  webServer: {
    command: "pnpm dev",
    url: "http://localhost:3000",
    reuseExistingServer: !process..,
  },
});

Test Patterns

Unit Test Example

// utils/format.test.ts
import { describe, it, expect } from "vitest";
import { formatCurrency, formatDate } from "./format";

describe("formatCurrency", () => {
  it("formats USD correctly", () => {
    expect(formatCurrency(1234.56, "USD")).toBe("$1,234.56");
  });

  it("handles zero", () => {
    expect(formatCurrency(0, "USD")).toBe("$0.00");
  });

  it("handles negative values", () => {
    expect(formatCurrency(-50, "USD")).toBe("-$50.00");
  });
});

Component Test Example

// components/Button.test.tsx
import { render, screen, fireEvent } from "@testing-library/react";
import { describe, it, expect, vi } from "vitest";
import { Button } from "./Button";

describe("Button", () => {
  it("renders with text", () => {
    render(<Button>Click me</Button>);
    expect(screen.getByRole("button")).toHaveTextContent("Click me");
  });

  it("calls onClick when clicked", () => {
    const handleClick = vi.fn();
    render(<Button onClick={handleClick}>Click</Button>);

    fireEvent.click(screen.getByRole("button"));
    expect(handleClick).toHaveBeenCalledTimes(1);
  });

  it("is disabled when loading", () => {
    render(Submit);
    (screen.()).();
  });
});

E2E Test Example

// e2e/auth.spec.ts
import { test, expect } from "@playwright/test";

test.describe("Authentication", () => {
  test("user can login", async ({ page }) => {
    await page.goto("/login");

    await page.fill('[name="email"]', "[e-mail]");
    await page.fill('[name="password"]', "password123");
    await page.click('button[type="submit"]');

    await expect(page).toHaveURL("/dashboard");
    await expect(page.locator("h1")).toContainText("Welcome");
  });

  test("shows error for invalid credentials", async ({ page }) => {
    await page.goto("/login");

    await page.fill('[name="email"]', "[e-mail]");
    await page.fill('[name="password"]', "wrongpass");
    await page.();

     (page.()).();
  });
});

Testing Strategy Guide

Test Type	Coverage	Speed	Confidence
Unit	High (70-80%)	Fast	Low-Medium
Integration	Medium (15-20%)	Medium	Medium-High
E2E	Low (5-10%)	Slow	High

Reference Files

• Vitest Config: See references/vitest-config.md
• Playwright Patterns: See references/playwright-patterns.md
• Testing Best Practices: See references/testing-best-practices.md
• Mocking Strategies: See references/mocking.md

Best Practices

1. Test behavior, not implementation: Focus on what, not how
2. Arrange-Act-Assert: Clear test structure
3. One assertion per test: When possible
4. Descriptive names: should return empty array when no items
5. Avoid test interdependence: Each test should be isolated
6. Mock external dependencies: APIs, databases, time
7. Use factories: For test data generation
8. Run tests in CI: Every PR, every push