Introduction

Mocking Strategies

There are mainly two mocking strategies:

Generally, mocking is the action of substituting a piece of software with another, seemingly compatible piece.
In other words, mocking means replacing one or more functions with a fake copy.
It aims at replacing the outgoing dependencies of our tests.
No request is actually made by the client to the server. Instead, the request is made to the client itself.
It alters the actual code under test.
Eg: fetch(url) { return new Response('hello') }
The above piece of code will always return a mocked response whenever fetch is called.
Libraries like MirageJS and Axios (interceptor) can help us achieve client-side mocking by providing a fake response.

Generally, stubbing means replacing some external service, or a network response, with a fake version.
It aims at replacing incoming dependencies, like a network response.
Here, a request is made by the client to the server.
It doesn't alter the actual code under test.
Eg: fetch(url) { return response.json(); }
The above piece of code will always return a response from the server whenever fetch is called.
Libraries like JSON-Server can help us achieve server-side mocking.

A mock API is a mocked-up/fake API.
It simulates/imitates the fetching of data from a fake server (from a specific route/endpoint) and returns the response.
This process is called API mocking (also called mocking an API response) Eg: JSON-server, JSON-server-graphql, Mockoon
Mock APIs are very useful in testing our code.

Mock APIs are very convenient to make HTTP calls/requests.
Real APIs could be a paid service. They are rate-limited (like only a few requests per day) and are very slow.

Mirage.js is an API Mocking Library which helps us mock an API response.
It helps us to create fake backend APIs easily.
Mirage.js is a client-side mocking framework. This means that it mocks APIs only in the browser.

Mirage.js sets up a “fake” server to serve as if in production without actually setting up a real server and thus helps us to create fake backend APIs.
When a request is sent by the client, Mirage JS intercepts it and provides a fake response.
Eg: We can intercept the call to the endpoint /api/users/ with Mirage.js, and then return a fake response.