
In this blog, we will explore a few of the most commonly used tools in REST API testing and how to use some of their most important features, in addition to determining which one suits a development process the best.
Swagger is an API specification & Postman is an API Client and appropriate for API first development while,
Postman is appropriate for testing such API based on specifications.
Swagger:

When speaking of Swagger we are referring to a set of rules, specifications, and tools that help us document our APIs.
In this manner, we can create documentation that is actually useful for people who need it. Swagger helps us create documentation that everyone can understand.
The most important of them is that everyone, or almost everyone, understands Swagger.
Whether you are a developer or have little development knowledge, you will be able to understand it thanks to Swagger UI.
Even machines can read it, turning it into another very attractive advantage. With Swagger, documentation can be used directly to automate API-dependent processes.
Another advantage is that we can find it integrated into popular, powerful tools such as those of WSO2. Lastly, we cannot forget either about the tools it provides.
Some of the most notable things that Swagger can help specify are:
Request types such as GET, POST, or PUT.
Request paths (URLs).
Parameters with respective names or descriptions.
Examples of bodies or associated definitions.
Expected responses.
Configuration:

The following dependencies would need to be installed on your machine before downloading and running the Swagger Codegen:- Java, version 7 or higher
Add some of these dependencies in your project while using swagger in the project:

Swagger UI allows the development team to visualize and interact with the API’s resources without having any of the implementation logic in place.
Benifits provide by the swagger:
Swagger does the documentation in a standard way (OpenAPI) means in a machine-readable language. So if you start documenting first, Swagger will write the structure of the API automatically based on this documentation.
The logic of the API is only dependent on developer and business requirements but the structure will be written by Swagger itself.
You don’t need an application to test your APIs. Just configure the Swagger once in your project and access it through a URL always with your project URL even on the production environment and test your APIs easily.
Testing is always a crucial part both on the developer level and on the QA engineer level.
Swagger provides you a UI integrated with your project with a URL accessible page where all the API methods will be listed down and you can test any method you want from that UI.
Swagger provides you the way to automate the documentation which means it picks up the methods with Get, Put, Post, Delete attributes and prepares the documentation by itself. And as you have done any change to any method, Swagger documentation will automatically be updated.
Postman

A postman is a web-based tool, so users will be able to access and work with API’s anywhere they can get an internet connection.
For new users, Postman also provides thorough documentation and web tutorials that make it easy to learn to use the tool.
Additionally, Postman provides sharing features that make it simple to share HTTP calls with other members of an organization.
Some of Postman’s features include:
Widespread features:
Some of these include executing all types of supported HTTP-supported requests, handling JSON, XML, Plain Text body requests, multiple headers or parameters, and validations of subsequent responses with JavaScript, such as expected status codes, expected body requests, parameters, and headers, among many others.
Collections:
Folder structured components that will hold a group of requests to be executed.
These collections can be divided as per each user’s necessities whether it’s by server, functionality, business-related needs, or others.

Environments:
In Postman, environments serve as global variables, which are key-value paired groups of information that will serve as static or dynamic information across all requests being executed with that specific key.

Get Request:
Once we send the get request, the server will return the response with status code 200.
That means the server has successfully returned the resources. In our case, we fetch the records of users so the server sent us a list of the user object.

Post Request:
At a high level, you can use it to send a post request to your web server and it gives you the response back.
It allows you to set up all the headers and cookies your API expects, then check the response when it comes back.
A common example of this is when you send a request to an API and get a response back, you verify that it returns an HTTP 200 OK status, or you make sure that the response contains a certain string in it.

Features provided by the Postman:
Easy test suite creation.
Users can store information to run tests in different environments.
Users can store data to use in other tests.
Integrates with Jenkins using Newman’s command-line tool.
It can move tests and environments to code repositories easily.
Conclusion:
Swagger is an open-source product that businesses can access for free and Postman is available for free for independent and small development teams.
