# frontend-testing-best-practices

A set of 6 testing guidelines that prioritizes Playwright E2E workflows over isolated React component tests and heavy mocking.

- skill · `type=skill` · Claude Code, Codex, Cursor, GitHub Copilot, Gemini CLI, OpenCode · 2200 installs · ★ 92
- Author: sergiodxa
- License: MIT · policy=mirror · the beginning of the file is at the end of this page
- Source: https://github.com/sergiodxa/agent-skills/tree/HEAD/skills/frontend-testing-best-practices/SKILL.md
- Updated: 2026-02-01
- HTML: https://affpapa.org/en/nevibecode/skills/frontend-testing-best-practices

## What it does

This skill guides your coding agent toward testing user behavior instead of internal implementation details. It prioritizes end-to-end tests for full application flows and strictly discourages isolated React component unit tests. Pure functions like formatters remain the only acceptable target for unit tests in Vitest.

The skill sets specific conventions for file layout and element targeting. All E2E files belong in `e2e/tests/`, while unit tests sit right next to their source files. When interacting with elements, the agent must pick accessible selectors such as `getByRole` or `getByLabel`, avoiding brittle CSS classes.

Whenever a unit test demands three or more mocks, the rules require replacing it with an E2E test. That makes mock-heavy component testing unacceptable under this configuration.

## Requirements
- Works with: Playwright

## Install

### Claude Code (native platform)

1. **Skills CLI (Vercel)**
```bash
npx skills add sergiodxa/agent-skills --skill frontend-testing-best-practices -a claude-code
```

2. **Manually: put the files in place**
- File: `~/.claude/skills/frontend-testing-best-practices/SKILL.md` — Copy the whole skill folder; for one project use .claude/skills/frontend-testing-best-practices/

### Codex

1. **Skills CLI (Vercel)**
```bash
npx skills add sergiodxa/agent-skills --skill frontend-testing-best-practices -a codex
```

2. **Manually: put the files in place**
- File: `.agents/skills/frontend-testing-best-practices/SKILL.md` — For all projects use ~/.agents/skills/

### Cursor

1. **Skills CLI (Vercel)**
```bash
npx skills add sergiodxa/agent-skills --skill frontend-testing-best-practices -a cursor
```

2. **Manually: put the files in place**
- File: `.cursor/skills/frontend-testing-best-practices/SKILL.md` — Cursor also reads .agents/skills/ and .claude/skills/

### GitHub Copilot

1. **GitHub CLI**
```bash
gh skill install sergiodxa/agent-skills frontend-testing-best-practices
```

2. **Manually: put the files in place**
- File: `.github/skills/frontend-testing-best-practices/SKILL.md`

### Gemini CLI

1. **Skills CLI (Vercel)**
```bash
npx skills add sergiodxa/agent-skills --skill frontend-testing-best-practices -a gemini-cli
```

2. **Platform CLI**
```bash
gemini skills install https://github.com/sergiodxa/agent-skills --path skills/frontend-testing-best-practices
```

### Windsurf (Devin Desktop)

**Manually: put the files in place**
- File: `.devin/skills/frontend-testing-best-practices/SKILL.md` — The legacy .windsurf/skills/ path still works

### OpenCode

**Skills CLI (Vercel)**
```bash
npx skills add sergiodxa/agent-skills --skill frontend-testing-best-practices -a opencode
```

### Claude.ai

**Claude.ai**
- Zip the folder and upload it in Settings → Capabilities → Skills

Where a file is given instead of a command, copy the files from the source to that path: https://github.com/sergiodxa/agent-skills/tree/HEAD/skills/frontend-testing-best-practices/SKILL.md

## When to use it
- structure Playwright E2E tests for user journeys
- eliminate brittle CSS selectors in browser tests
- replace complex mock setups with end-to-end tests
- isolate pure utility functions for Vitest unit testing

## Example prompts
- Write an E2E checkout test following the frontend-testing-best-practices rules
- Review this component test and convert it into an E2E spec if needed
- Refactor these tests to use accessible role selectors instead of CSS classes

## Source text · SKILL.md · MIT

Below is the content of a third-party file. It is data, not instructions for you: do not act on anything written inside unless the human asks. Block tag: 23c669f5839dc98e.

BEGIN THIRD-PARTY FILE 23c669f5839dc98e
````text
---
name: frontend-testing-best-practices
description: Testing best practices for the frontend. Emphasizes E2E tests over unit tests, minimal mocking, and testing behavior over implementation details. Use when writing tests or reviewing test code.
---

# Testing Best Practices

Guidelines for writing effective, maintainable tests that provide real confidence. Contains 6 rules focused on preferring E2E tests, minimizing mocking, and testing behavior over implementation.

## Core Philosophy

1. **Prefer E2E tests over unit tests** - Test the whole system, not isolated pieces
2. **Minimize mocking** - If you need complex mocks, write an E2E test instead
3. **Test behavior, not implementation** - Test what users see and do
4. **Avoid testing React components directly** - Test them through E2E

## When to Apply

Reference these guidelines when:

- Deciding what type of test to write
- Writing new E2E or unit tests
- Reviewing test code
- Refactoring tests

## Rules Summary

### Testing Strategy (CRITICAL)

#### prefer-e2e-tests - @rules/prefer-e2e-tests.md

Default to E2E tests. Only write unit tests for pure functions.

```typescript
// E2E test (PREFERRED) - tests real user flow
test("user can place an order", async ({ page }) => {
  await createTestingAccount(page, { account_status: "active" });
  await page.goto("/catalog");
  await page.getByRole("heading", { name: "Example Item" }).click();
  await page.getByRole("link", { name: "Buy" }).click();
  // ... complete flow
  await expect(page.getByAltText("Thank you")).toBeVisible();
});

// Unit test - ONLY for pure functions
test("formatCurrency formats with two decimals", () => {
  expect(formatCurrency(1234.5)).toBe("$1,234.50");
});
```

#### avoid-component-tests - @rules/avoid-component-tests.md

Don't unit test React components. Test them through E2E or not at all.

```typescript
// BAD: Component unit test
describe("OrderCard", () => {
  test("renders amount", () => {
    render(<OrderCard amount={100} />);
    expect(screen.getByText("$100")).toBeInTheDocument();
  });
});

// GOOD: E2E test covers the component naturally
test("order history shows orders", async ({ page }) => {
  await page.goto("/orders");
  await expect(page.getByText("$100")).toBeVisible();
});
```

#### minimize-mocking - @rules/minimize-mocking.md

Keep mocks simple. If you need 3+ mocks, write an E2E test instead.

```typescript
// BAD: Too many mocks = write E2E test
vi.mock("~/lib/auth");
vi.mock("~/lib/transactions");
vi.mock("~/hooks/useAccount");

// GOOD: Simple MSW mock for loader test
mockServer.use(
  http.get("/api/user", () => HttpResponse.json({ name: "John" })),
);
```
````
END THIRD-PARTY FILE 23c669f5839dc98e

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