What is a Mock API? Mocking Explained with Examples

The short answer: A mock API is a simulated version of a real API, used primarily for testing and development.

The slightly longer answer: The mock API mimics the behavior of the actual API by providing realistic responses to requests, which enables developers to validate their code under real-world-like conditions even when the actual API is unavailable. Mock APIs can be locally hosted or on the network, depending on the requirements of the unit or integration tests being conducted.

When would you mock an API?

1. Parallel development: When frontend and backend teams are working simultaneously, the frontend team can use a mock API to simulate the backend responses. This allows both teams to work independently and speeds up the development process. {give a practical example}
2. Third-party services: If your application depends on an external third-party service, using a mock API can help during development and testing to avoid overuse or misuse of the third-party services, which may be cost-prohibitive or against their terms of service.
3. Unstable or unavailable services: If a service (or sandbox) you depend on is unstable or frequently unavailable, a mock API can provide a more reliable development environment and ensure that your testing isn't blocked by these issues.

Building a Mock API: An Example

Building a mock API involves simulating the behaviors of an actual API — defining endpoints, methods, request parameters, and corresponding responses. Let’s use a hypothetical scenario to illustrate the process.

Let's say we have a development team working on a new feature for an e-commerce application, specifically a 'Recommended Products' feature that suggests items to users based on their browsing history. This feature relies on a yet-to-be-built 'Recommendation Engine' API that the backend team is developing.

Here's a simplified step-by-step process to set up the mock API:

Step 1: Define the API Endpoints and Methods

The first step in creating a mock API is to identify and define the endpoints and methods that the actual API will have. In our scenario, the endpoint could be something like /api/recommendations with a GET method. This endpoint will return a list of recommended products.

Step 2: Identify Request Parameters

To build a simulation that’s close to the real thing, we’ll want to identify any request parameters that the actual API will expect. These parameters could be sent in the URL or the request body, depending on the API's design. In our case, the 'Recommendation Engine' API might require a userId parameter to generate personalized recommendations.

Step 3: Define the Responses

Define what the API's responses will look like. This includes the status codes, headers, and response bodies. For instance, a successful response from our 'Recommendation Engine' API might return a 200 OK status code, standard headers, and a response body containing an array of product IDs.

Step 4: Set Up the Mock API

Now it's time to implement the mock API. Using a service like WireMock Cloud, you can input the endpoints, methods, request parameters, and responses you defined earlier. Once set up, the mock API will respond to incoming requests as if it were the real API.

Step 5: Test and Refine

Finally, the development team can use the mock API to develop and test the 'Recommended Products' feature. As the backend team progresses with the actual 'Recommendation Engine' API, the mock API can be updated to reflect any changes, ensuring the mock remains a reliable stand-in throughout the development process.

Next: Read about different types of API mocking tools

‍