adaptationio/component-testing

Component Testing with Playwright

Test UI components in isolation using Playwright's experimental component testing feature. Supports React, Vue, Svelte, and Solid.

Quick Start

// Button.spec.tsx
import { test, expect } from '@playwright/experimental-ct-react';
import { Button } from './Button';

test('button click triggers callback', async ({ mount }) => {
  let clicked = false;

  const component = await mount(
    <Button onClick={() => clicked = true}>Click me</Button>
  );

  await component.click();
  expect(clicked).toBe(true);
});

Installation

React

npm init playwright@latest -- --ct
# Select React when prompted

Or manually:

npm install -D @playwright/experimental-ct-react

Vue

npm install -D @playwright/experimental-ct-vue

Svelte

npm install -D @playwright/experimental-ct-svelte

Configuration

playwright-ct.config.ts:

import { defineConfig, devices } from '@playwright/experimental-ct-react';

export default defineConfig({
  testDir: './src',
  testMatch: '**/*.spec.tsx',

  use: {
    ctPort: 3100,
    ctViteConfig: {
      // Custom Vite config for component tests
    },
  },

  projects: [
    {
      name: 'chromium',
      use: { ...devices['Desktop Chrome'] },
    },
    {
      name: 'firefox',
      use: { ...devices['Desktop Firefox'] },
    },
    {
      name: 'webkit',
      use: { ...devices['Desktop Safari'] },
    },
  ],
});

React Component Testing

Basic Mount

import { test, expect } from '@playwright/experimental-ct-react';
import { UserCard } from './UserCard';

test('displays user info', async ({ mount }) => {
  const component = await mount(
    <UserCard
      name="John Doe"
      email="[email protected]"
    />
  );

  await expect(component.getByText('John Doe')).toBeVisible();
  await expect(component.getByText('[email protected]')).toBeVisible();
});

With Props

test('button variants', async ({ mount }) => {
  // Primary variant
  const primary = await mount(<Button variant="primary">Save</Button>);
  await expect(primary).toHaveClass(/btn-primary/);

  // Secondary variant
  const secondary = await mount(<Button variant="secondary">Cancel</Button>);
  await expect(secondary).toHaveClass(/btn-secondary/);
});

With Event Handlers

test('form submission', async ({ mount }) => {
  const submittedData: any[] = [];

  const component = await mount(
    <ContactForm onSubmit={(data) => submittedData.push(data)} />
  );

  await component.getByLabel('Name').fill('John');
  await component.getByLabel('Email').fill('[email protected]');
  await component.getByRole('button', { name: 'Submit' }).click();

  expect(submittedData).toHaveLength(1);
  expect(submittedData[0]).toEqual({
    name: 'John',
    email: '[email protected]',
  });
});

With Context Providers

// Create wrapper for providers
import { ThemeProvider } from './ThemeContext';

test('themed component', async ({ mount }) => {
  const component = await mount(
    <ThemeProvider theme="dark">
      <ThemedButton>Click</ThemedButton>
    </ThemeProvider>
  );

  await expect(component).toHaveClass(/dark-theme/);
});

With Slots/Children

test('card with custom content', async ({ mount }) => {
  const component = await mount(
    <Card>
      <CardHeader>Title</CardHeader>
      <CardBody>Content here</CardBody>
      <CardFooter>
        <Button>Action</Button>
      </CardFooter>
    </Card>
  );

  await expect(component.getByText('Title')).toBeVisible();
  await expect(component.getByText('Content here')).toBeVisible();
  await expect(component.getByRole('button')).toBeVisible();
});

Vue Component Testing

// Counter.spec.ts
import { test, expect } from '@playwright/experimental-ct-vue';
import Counter from './Counter.vue';

test('counter increments', async ({ mount }) => {
  const component = await mount(Counter, {
    props: {
      initialCount: 0,
    },
  });

  await expect(component.getByText('Count: 0')).toBeVisible();
  await component.getByRole('button', { name: '+' }).click();
  await expect(component.getByText('Count: 1')).toBeVisible();
});

With Slots

test('card with slots', async ({ mount }) => {
  const component = await mount(Card, {
    slots: {
      default: '<p>Card content</p>',
      header: '<h2>Card Title</h2>',
    },
  });

  await expect(component.getByText('Card Title')).toBeVisible();
  await expect(component.getByText('Card content')).toBeVisible();
});

With Vuex/Pinia

import { test, expect } from '@playwright/experimental-ct-vue';
import { createTestingPinia } from '@pinia/testing';
import UserProfile from './UserProfile.vue';

test('displays user from store', async ({ mount }) => {
  const component = await mount(UserProfile, {
    global: {
      plugins: [
        createTestingPinia({
          initialState: {
            user: { name: 'John', email: '[email protected]' },
          },
        }),
      ],
    },
  });

  await expect(component.getByText('John')).toBeVisible();
});

Svelte Component Testing

// Button.spec.ts
import { test, expect } from '@playwright/experimental-ct-svelte';
import Button from './Button.svelte';

test('button emits click', async ({ mount }) => {
  let clicked = false;

  const component = await mount(Button, {
    props: {
      label: 'Click me',
    },
    on: {
      click: () => clicked = true,
    },
  });

  await component.click();
  expect(clicked).toBe(true);
});

Testing Patterns

Visual Regression

test('button visual states', async ({ mount }) => {
  const component = await mount(<Button>Click</Button>);

  // Default state
  await expect(component).toHaveScreenshot('button-default.png');

  // Hover state
  await component.hover();
  await expect(component).toHaveScreenshot('button-hover.png');

  // Focus state
  await component.focus();
  await expect(component).toHaveScreenshot('button-focus.png');
});

Accessibility

import AxeBuilder from '@axe-core/playwright';

test('button is accessible', async ({ mount, page }) => {
  await mount(<Button>Submit</Button>);

  const results = await new AxeBuilder({ page }).analyze();
  expect(results.violations).toEqual([]);
});

Responsive Behavior

test('responsive navigation', async ({ mount, page }) => {
  const component = await mount(<Navigation />);

  // Desktop - horizontal nav
  await page.setViewportSize({ width: 1280, height: 720 });
  await expect(component.locator('.nav-horizontal')).toBeVisible();

  // Mobile - hamburger menu
  await page.setViewportSize({ width: 375, height: 667 });
  await expect(component.locator('.hamburger-menu')).toBeVisible();
});

Loading States

test('async component states', async ({ mount }) => {
  const component = await mount(<DataTable dataUrl="/api/data" />);

  // Loading state
  await expect(component.getByText('Loading...')).toBeVisible();

  // Wait for data
  await expect(component.getByRole('table')).toBeVisible();
  await expect(component.getByText('Loading...')).not.toBeVisible();
});

Error States

test('error handling', async ({ mount, page }) => {
  // Mock failed API
  await page.route('**/api/data', route => {
    route.fulfill({ status: 500 });
  });

  const component = await mount(<DataTable dataUrl="/api/data" />);

  await expect(component.getByText(/error/i)).toBeVisible();
  await expect(component.getByRole('button', { name: 'Retry' })).toBeVisible();
});

Hooks and Fixtures

Before Each Test

import { test as base, expect } from '@playwright/experimental-ct-react';

const test = base.extend({
  autoMockApi: async ({ page }, use) => {
    await page.route('**/api/**', route => {
      route.fulfill({ status: 200, body: '{}' });
    });
    await use();
  },
});

test('component with mocked api', async ({ mount, autoMockApi }) => {
  const component = await mount(<ApiComponent />);
  // API calls are automatically mocked
});

Custom Mount

const test = base.extend({
  mountWithProviders: async ({ mount }, use) => {
    const wrappedMount = async (component: JSX.Element) => {
      return mount(
        <ThemeProvider>
          <AuthProvider>
            {component}
          </AuthProvider>
        </ThemeProvider>
      );
    };
    await use(wrappedMount);
  },
});

test('with providers', async ({ mountWithProviders }) => {
  const component = await mountWithProviders(<Dashboard />);
  // Component has access to theme and auth contexts
});

Running Tests

# Run all component tests
npx playwright test -c playwright-ct.config.ts

# Run specific test file
npx playwright test Button.spec.tsx -c playwright-ct.config.ts

# Run with UI mode
npx playwright test -c playwright-ct.config.ts --ui

# Update snapshots
npx playwright test -c playwright-ct.config.ts --update-snapshots

Best Practices

1. Test behavior, not implementation - Focus on user interactions
2. Keep components isolated - Mock external dependencies
3. Test all states - Default, loading, error, empty, success
4. Use semantic queries - getByRole, getByLabel over CSS selectors
5. Combine with E2E - Component tests for logic, E2E for integration

References

• references/react-patterns.md - React-specific testing patterns
• references/vue-patterns.md - Vue-specific testing patterns