do we need to test db with api automation code example

Example 1: when code not ready how to test in api

I would mock it with Postman
and swap the base url when it's ready

Example 2: why do you do rest api teting

The purpose of rest api testing is to record the response of rest api 
by sending various HTTP/S requests to check if rest api is working fine or not. 
Rest api testing is done by GET, POST, PUT and DELETE methods.

Rest stands for Representational State Transfer. It is an architectural style 
and an approach for communication used in the development of Web Services. 
REST has become a logical choice for building APIs. It enables users 
to connect and interact with cloud services efficiently.