Mocking WebSocket APIs with Mock Service Worker

In this course, you'll learn to use Mock Service Worker (MSW) to intercept and handle WebSocket connections.

While building a simple chat application, we'll cover the basics of intercepting and mocking WebSocket traffic with MSW. You'll learn to:

• Capture specific incoming and outgoing messages
• Mock client and server events
• Simulate multiple WebSocket clients

These fundamentals will give you a starting point for developing and testing WebSocket interactions.

Handling Edge Cases

We’ll explore non-trivial challenges when developing and testing WebSocket apps, such as:

• Ensuring type-safe WebSocket communication with Zod
• Dealing with unexpected disconnections
• Mocking error scenarios

By facing these issues in a controlled environment, you'll be better prepared to handle them in your own projects.

Using Mocks as a Proxy

We'll demonstrate how to use MSW alongside a real WebSocket server. You'll see how to:

• Selectively forward messages to the server
• Modify message content in transit
• Reproduce and prevent server closures

This will give you a clearer picture of how MSW fits into a real-world setup.

Writing Meaningful Tests

Finally, we'll put our MSW skills to use by writing some practical tests, including:

• Integration tests with Vitest
• Simple end-to-end tests with Playwright

We are going to focus on how to integrate MSW into your test suite, and see how to use the same event handlers to test WebSocket-dependent components and user flows.

Is This Course Right for You?

This course is aimed at developers who work with WebSocket-heavy applications and want to improve their testing strategies. It assumes basic familiarity with JavaScript testing frameworks.

While the course uses specific tools like Vitest and Playwright, the concepts can be adapted to your preferred setup.

At the end of the course, you'll have experience using MSW to test a variety of WebSocket scenarios. Let's dive in and start learning!