The Complete Guide to Testing ChatGPT Apps and MCP Apps

[Updated 2026-02-05] Testing ChatGPT Apps presents unique challenges. Your UI runs inside an AI host’s runtime, responds to tool invocations, and adapts to multiple display modes and themes. Without proper testing infrastructure, you’re deploying blind.

TL;DR: Use sunpeak’s built-in testing with Vitest for unit tests (pnpm test) and Playwright for e2e tests (pnpm test:e2e). Define states in simulation files, test across display modes with createSimulatorUrl, and run everything in CI.

This guide covers everything you need to test ChatGPT Apps with confidence.

Why Testing ChatGPT Apps is Different

ChatGPT Apps run in a specialized runtime environment. Your React components don’t just render in a browser—they render inside the ChatGPT App runtime with:

• Host frontend state - Inline, in picture-in-picture, and fullscreen display modes, light or dark theme, etc.
• Tool invocations - The AI host calls your app’s tools with specific inputs
• Backend state - Various possible states for users and sessions in your database
• App state - Persistent state that survives across invocations

Testing each combination manually isn’t feasible, the combinatorics are brutal. You need automated testing that covers all these scenarios.

Setting Up Your Testing Environment

If you’re using the sunpeak ChatGPT App framework, testing is pre-configured. Start with:

pnpm add -g sunpeak && sunpeak new
cd my-app

Your project includes:

• Vitest configured with jsdom, React Testing Library, and jest-dom matchers
• Playwright configured to test against the ChatGPT App simulator
• Simulation files in tests/simulations/ for deterministic states

Unit Testing with Vitest

Unit tests validate individual components in isolation. Run them with:

pnpm test

Create tests alongside your components in src/resources with the .test.tsx extension:

import { render, screen } from '@testing-library/react';
import { Counter } from '../src/resources/counter-resource';

describe('Counter', () => {
  it('renders the initial count', () => {
    render(<Counter />);
    expect(screen.getByText('0')).toBeInTheDocument();
  });

  it('increments when button is clicked', async () => {
    render(<Counter />);
    await userEvent.click(screen.getByRole('button', { name: /increment/i }));
    expect(screen.getByText('1')).toBeInTheDocument();
  });
});

Unit tests run fast and catch component-level bugs early. They’re ideal for testing:

• Component rendering logic
• User interactions within a component
• Props and state handling

End-to-End Testing with Playwright

E2E tests validate your ChatGPT App running in the simulator. Run them with:

pnpm test:e2e

Create tests in tests/e2e/ with the .spec.ts extension:

import { test, expect } from '@playwright/test';
import { createSimulatorUrl } from 'sunpeak';

test('counter increments in fullscreen mode', async ({ page }) => {
  await page.goto(createSimulatorUrl({
    simulation: 'counter-show',
    displayMode: 'fullscreen',
    theme: 'dark',
  }));

  await page.getByRole('button', { name: /increment/i }).click();
  await expect(page.getByText('1')).toBeVisible();
});

The createSimulatorUrl utility generates URLs with your test configuration:

• simulation - Your simulation file name (sets initial state)
• displayMode - inline, pip, or fullscreen (tests display adaptation)
• theme - light or dark (tests theme handling)
• deviceType - mobile, tablet, desktop, or unknown (tests responsive behavior)
• touch / hover - Enable or disable touch/hover capabilities
• safeAreaTop, safeAreaBottom, etc. - Simulate device notches and insets

Creating Simulation Files

Simulation files define deterministic states for testing. Create them in tests/simulations/{resource-name}/:

{
  "userMessage": "Show me a counter starting at 5",
  "tool": {
    "name": "show_counter",
    "description": "Displays an interactive counter",
    "inputSchema": {
      "type": "object",
      "properties": {
        "initialCount": { "type": "number" }
      }
    }
  },
  "toolInput": {
    "arguments": { "initialCount": 5 }
  },
  "toolResult": {
    "content": [{ "type": "text", "text": "Counter displayed" }],
    "structuredContent": {
      "count": 5
    }
  }
}

This simulation:

• Shows userMessage in the simulator chat interface
• Defines the tool with its name and input schema
• Sets toolInput with mock input accessible via useToolData()
• Provides toolResult with mock output data passed to your component via useToolData()

Use simulations to test specific states without manual setup:

// Test the counter with toolResult.structuredContent.count = 5
await page.goto(createSimulatorUrl({ simulation: 'counter-show' }));
await expect(page.getByText('5')).toBeVisible();

// Test a different initial state
await page.goto(createSimulatorUrl({ simulation: 'counter-initial' }));
await expect(page.getByText('0')).toBeVisible();

Testing Across Display Modes

ChatGPT Apps appear in three display modes. Test all of them:

const displayModes = ['inline', 'pip', 'fullscreen'] as const;

for (const displayMode of displayModes) {
  test(`renders correctly in ${displayMode} mode`, async ({ page }) => {
    await page.goto(createSimulatorUrl({
      simulation: 'counter-show',
      displayMode,
    }));

    await expect(page.getByRole('button')).toBeVisible();
  });
}

Each mode has different constraints:

• Inline - Limited height, embedded in chat
• Picture-in-picture - Floating window, can be repositioned
• Fullscreen - Maximum space, modal overlay

Your app should adapt gracefully to each.

Testing Theme Adaptation

Test both light and dark themes:

test('adapts to dark theme', async ({ page }) => {
  await page.goto(createSimulatorUrl({
    simulation: 'counter-show',
    theme: 'dark',
  }));

  // Verify dark theme styles are applied
  const button = page.getByRole('button');
  await expect(button).toHaveCSS('background-color', 'rgb(255, 184, 0)');
});

Running Tests in CI/CD

Add testing to your GitHub Actions workflow:

name: Test
on: [push, pull_request]

jobs:
  test:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4
      - uses: pnpm/action-setup@v2
      - uses: actions/setup-node@v4
        with:
          node-version: '20'
          cache: 'pnpm'

      - run: pnpm install
      - run: pnpm test
      - run: pnpm exec playwright install --with-deps
      - run: pnpm test:e2e

Playwright tests automatically:

1. Start the sunpeak dev server
2. Wait for it to be ready
3. Run tests against the ChatGPT App simulator
4. Shut down when complete

Debugging Failing Tests

When tests fail, use these debugging techniques:

Playwright Debug Mode

pnpm test:e2e --ui

Opens a visual debugger where you can:

• Step through tests
• Inspect the DOM at each step
• See screenshots and traces

Vitest Verbose Output

pnpm test --reporter=verbose

Shows detailed output including:

• Individual assertion results
• Component render output
• Error stack traces

Screenshot on Failure

Playwright automatically captures screenshots on failure. Find them in test-results/.

Testing Best Practices

One assertion per test. Keep tests focused and easy to debug:

// Good: focused test
test('increment button is visible', async ({ page }) => {
  await page.goto(createSimulatorUrl({ simulation: 'counter-show' }));
  await expect(page.getByRole('button', { name: /increment/i })).toBeVisible();
});

// Avoid: multiple unrelated assertions
test('counter works', async ({ page }) => {
  // Too many things being tested at once
});

Test behavior, not implementation. Focus on what users see:

// Good: tests user-visible behavior
await expect(page.getByText('5')).toBeVisible();

// Avoid: tests implementation details
await expect(component.state.count).toBe(5);

Use descriptive test names. Make failures self-explanatory:

// Good: clear failure message
test('displays error message when API call fails', ...)

// Avoid: vague description
test('handles error', ...)

Clean up between tests. Reset state to avoid test pollution:

afterEach(async () => {
  // Reset any global state
});

Next Steps

Testing is essential for shipping reliable ChatGPT Apps. With sunpeak’s ChatGPT App testing infrastructure, you can:

• Run unit tests with Vitest for fast feedback
• Run e2e tests with Playwright for full integration coverage
• Test across display modes, themes, and device types
• Integrate testing into your CI/CD pipeline

Get started with sunpeak:

pnpm add -g sunpeak && sunpeak new

• Learn about the ChatGPT App framework
• Read the testing documentation
• Try the interactive simulator
• Star sunpeak on GitHub