Testing API Endpoints with a Stub Server in Jest (TypeScript)

Testing API integrations can be tricky, especially when dealing with external dependencies. Creating a stub server allows you to isolate your code and test its behavior without relying on a real API, making your tests faster, more reliable, and easier to control. This challenge focuses on building a simple stub server using Node.js and testing it with Jest.

Problem Description

You need to create a minimal stub server using Node.js and the http module. This server should respond with a predefined JSON payload for a specific endpoint (/api/data). The goal is to create a server that can be easily mocked and tested within a Jest environment. Your task is to implement the server logic and then write a Jest test to verify that the server responds with the expected JSON data when the /api/data endpoint is accessed. The server should only handle GET requests.

Key Requirements:

• Endpoint: The server must respond to requests made to /api/data.
• Response: The server must respond with the following JSON payload: {"message": "Hello from the stub server!"}.
• HTTP Method: The server should only handle GET requests. Other methods should result in a 405 Method Not Allowed response.
• Error Handling: The server should handle invalid requests gracefully (e.g., requests to non-existent endpoints) and return a 404 Not Found response.
• TypeScript: The code must be written in TypeScript.

Expected Behavior:

• A GET request to /api/data should return a 200 OK status code and the specified JSON payload.
• A GET request to any other endpoint should return a 404 Not Found status code.
• A request with a method other than GET (e.g., POST, PUT, DELETE) to /api/data or any other endpoint should return a 405 Method Not Allowed status code.

Examples

Example 1:

Input: GET request to /api/data
Output: 200 OK, {"message": "Hello from the stub server!"}
Explanation: The server successfully handles the GET request to the defined endpoint and returns the expected JSON.

Example 2:

Input: GET request to /api/other-endpoint
Output: 404 Not Found
Explanation: The server does not have a handler for this endpoint and returns a 404 error.

Example 3:

Input: POST request to /api/data
Output: 405 Method Not Allowed
Explanation: The server only handles GET requests.  A POST request results in a 405 error.

Constraints

• The server should be lightweight and efficient.
• The code should be well-structured and easy to understand.
• The server should be written in TypeScript.
• The server should only listen on a single port (you don't need to specify the port in the code, it's for the Jest test to handle).

Notes

• You can use the built-in http module in Node.js to create the server.
• Consider using a simple routing mechanism to handle different endpoints.
• The Jest test will need to start the server, make a request to it, and then verify the response. You'll need to use a library like node-fetch or axios within your Jest test to make the HTTP request.
• Remember to properly handle errors and return appropriate status codes.
• Focus on creating a minimal, functional stub server that meets the specified requirements. Don't over-engineer the solution.