How to Use Postman for API Testing?

How to Use Postman for API Testing

APIs act as a medium that allows an application to communicate with other applications. Hence, testing and verifying the functionality, performance, safety and credibility of the application program interface is a given. These tests are conducted either as a part of integration testing or directly on the API. 

The API code is key to enabling the exchange of data across software programs. An API layer is a part of the numerous layers that applications have and they bank on the business logic of the application. They also focus on defining requests of how to create them and which data formats are in use. 

API testing using Postman is widely used for writing functional, integration, and regression tests. Postman for API testing enables HTTP clients who test HTTP requests, to use a GUI (Graphical User Interface), via which numerous forms of responses obtained have to be validated. One of the greatest advantages of using the Postman application is the collection feature that helps organise tests and the ability to test in different created environments. Additionally, it is user-friendly and time-saving.

Getting started with Postman – How to download and install Postman on your computer 

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(Source: https://www.pexels.com/photo/close-up-photo-of-programming-of-codes-546819/)

The Postman software has become a house name in software testing and is being used by globally accredited MNCs like Twitter, BetterCloud, Gear4music, Momentive and the like. With a substantial number of API tools in its arsenal, it helps enhance the development cycle, optimise design mockups etc and uses them on a web browser directly. There is also a downloadable desktop version you can use.

Learn how to setup Postman on your Mac or Windows computer by following the steps given below:-

Step 1: Postman is available to download as a native desktop app for Windows (Intel 32 or 64-bit), Mac (Apple silicon or Intel), and Linux (64-bit). Visit the link https://www.postman.com/ using any web browser and download the version you require. 

Step 2: Check your downloads folder for any executable file, unzip it if required and then run it. The software will open automatically after download enabling you to see the interface. 

Downloading Postman for Linux however, requires different steps. You can follow the below steps to setup Postman in your Linux system:-

Step 1: Manually download Postman using the command snap program or the Snap store link.

Step 2: Unzip the app, start it from a launcher icon, and make a desktop file named Postman.desktop and save it here:-

				
					~/.local/share/applications/Postman.desktop

				
			

Step 3: Enter the following in the file to replace /path/to/Downloads (note that ‘Downloads’ is the location of the file and can be changed as preferred), and then save:-

				
					[Desktop Entry]

Encoding=UTF-8

Name=Postman

Exec=/path/to/Downloads/Postman/app/Postman %U

Icon=/path/to/Downloads/Postman/app/resources/app/assets/icon.png

Terminal=false

Type=Application

Categories=Development;
				
			

Creating your first API request in Postman 

In API testing, API servers are used to establish online communication to enable testers to use one application to structurally access the workings and capabilities of a separate application. Typically, this communication happens over the internet by way of an API server. A client application usually sends the server a request which is further processed and returned with a response.

By using Postman you can both create and send API requests to an endpoint, extract data from a specific source, or test the credibility of an API. No terminal commands or codes are required. Postman only requires you to create a request and simply select Send.

A request must have an HTTP request method as well as the URL of an API endpoint. Postman testing offers the following endpoint modes of interaction:-

  • GET: Retrieve data from an API
  • POST: Send new data to an API
  • PUT: Replace existing data
  • PATCH: Update specific or existing data
  • DELETE: Remove existing data

To learn how to use Postman for API testing, you need to open Postman and perform the following actions:-

  • Select the + sign in the workbench. This will open a separate tab.
  • Enter postman-echo.com/get to get the request URL.
  • Click on Send.

You can additionally use the Postman Echo API to send more requests once you get a hang of this process. It is a useful tool that will enable you to test API requests in Postman.

Testing API endpoints with Postman 

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(Source: https://www.pexels.com/photo/codes-on-tilt-shift-lens-2004161/)

Testing is crucial in the process of API development. Postman enables developers to create a collection containing API tests and link them to the API. A Postman API test also comes with supporting CI (Continuous Integration) tools. To enhance the ease of adding and running an API test, Postman is the go-to software that developers use extensively. It additionally offers CI integration to view the build status or start new builds. Here is a detailed step-by-step process for adding tests, running tests and integrating CI in Postman: 

Adding API tests

For adding a test collection to an API, perform the following actions:-

  • Select an API from the ones in the sidebar 
  • Click on Test and Automation.
  • Beside Collections, click on the + sign and select:-

    – Add new collection: Makes a new empty collection in the API in which you can add tests in the Tests tab.
    – Copy existing collection: You can select any collection available from the list. A copy will be added to the API.
    – Generate from definition: Change any settings to personalize the new collection and click on Generate Collection.

Running API tests

After you add a test collection, you need to run it for an API test and view test results. Perform the following to run an API test in Postman:-

  • Select an API from the ones in the sidebar 
  • Click on Test and Automation.
  • Under Collections, click on Run to a test collection.
  • Click on any configuration options to run the collection and then click on Run API Tests. 
  • For a detailed view of the test results, you can expand the collection and click on View Report.

Adding CI integration

Continuous Integration and Continuous Delivery (CI/CD) tools are some of the widely used tools that Postman has integrated. After setting up CI integration for an API, one can easily view the builds’ status and even create a new build, with Postman. It is also easy to run API tests in Postman with the CI pipeline. Follow the steps below to integrate CI integration for API:-

  • Select an API from the ones in the sidebar 
  • Click on Test and Automation.
  • Under Automate, click on the CI integration of your choice.

Best practices for API testing with Postman 

Postman makes API testing easy. However, with the best practices, you can optimize API Postman Testing. Some of the best practices have been elucidated below:- 

‘Postman tutorial for API testing’

Know about application flow

The API specification document makes it a mandate for QAs to have a detailed understanding of the end-to-end flow of an application, and the testing scope to define the serial order of the requests that need to be executed.

Create Postman environments

To efficiently use the Postman tool for testing you need to know in detail about how to execute a request on various test environments (like Dev, Stage, QA, and Prod) without altering test requests. This helps reduce testing efforts and the number of requests.

Create a collection 

By creating a collection, one can organise API requests by storing them in their respective folders. This helps maintain requests with more efficiency. 

Define global level and local level variables 

One should be able to define test data in both local and global variables on the basis of where they can be used. These variables are used in the script, to make it legible and comprehensive. 

Write tests for every request 

Based on certain scenarios, you will be required to add requests and write tests under the Test tab to validate the response (response time, status code). Run these tests to get the request i.e the pass/fail status. 

Detect reusable functions 

Identifying and listing reusable functions can help in the reduction of repeated code and enhance maintainability. 

Add pre-request and post-request scripts

Pre-request and post-request scripts need to be added for enhanced execution. It also makes the execution report more readable and helps avoid request duplication. 

Define the sequence of test execution 

API sequencing in Postman helps execute API requests in sequential order making it easy for users to test the application’s end-to-end flow with just a single click. 

Prepare the test data 

It is crucial to detect and prepare test data to ensure that it covers both negative and positive use cases. It also helps in storing them in their respective files. 

Advanced features of Postman for API testing 

Testing API with Postman is widely preferred by developers to render better results. Not only does it facilitate sending and receiving requests from a service without requiring a framework but also comes with numerous advanced features dedicated to offering QAs with stellar testing experience. Some of the said advanced features include:-

Postman HTTP

HTTP requests are used to send information to APIs for a Rest API test. Postman uses HTTP messages sent from the client side to HTTP servers. In general, HTTP requests comprise the following:-

  • Start line
  • Set of HTTP headers
  • Body

The user-friendly interface of Postman enables developers to send simple requests by only entering them, filling in the required headers, choosing the HTTP method and clicking ‘send’. 

REST API test, Postman

REST stands for Representational State Transfer and refers to the architectural style used in distributed hypermedia systems. In a nutshell, REST designs the look of an API. It is more like a set of guidelines followed by developers while creating APIs. As per the said rules, you should be able to get a chunk of data once a specific URL is entered. REST is also a Postman API call that is widely used to create complicated requests, and enhance query execution, and response verification. 

Conclusion and final thoughts on the benefits of using Postman for API testing 

Postman is undoubtedly a handy tool created to provide software developers with the best testing experience. API testing using Postman API testing lets users store values and data variably at the environment level. These can further be used for sending any request’s URL, body and headers. Users can easily run automated API tests before code deployment in a user-friendly environment dedicated to efficient testing. It can fulfil any functionality that a developer might need. With more than 5 million users on a global scale per month, Postman has been deemed the most convenient tool that has made API development simple, easy, and most importantly efficient.

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