How to create a mock API code example

Example: when to use mock api

We can use mock API server during 
development and testing when live
data is unavailable or not reliable.
While developers designing the API
we can use mock API's to work on. 
Once end points are available we can
implement the endpoints to our test script. 
I am using Postman for mocking API. 
I create mock server with GET request
to postman-echo.com/get endpoint.