Deep Dive – API Testing Automation with Postman

API Testing
Automation
Quality Automation
by Meera Bagthaliya

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API automation using Postman

Highlights

  • Application Program Interface (API) automation is a no-code approach or low-code approach that works alongside the existing CI/CD processes. 
  • We can use Postman to automate various types of testing like unit testing, functional testing, integration testing, end-to-end testing, regression testing, mock testing, etc. 
  • API testing automation with postman can improve and increase the depth and scope of the tests to create top-notch quality software.

APIs facilitate communication between two applications; and API testing ensures the relay of messages between them is fast, secure, and reliable. API testing remains a crucial part of QA, DevOps, and development teams to help develop the continuous testing practice. Therefore, as a leading QA automation and test automation services firm, we recognize the importance of  API testing automation and its mindful implementation.

The API testing process starts with a clearly defined program scope and a comprehensive understanding on how APIs work. Some questions that testers need to consider here are — Which endpoints are available for testing? Which response codes are expected for successful or unsuccessful requests? Which error message could appear in the body of an unsuccessful request? Postman is an API client that helps the developers to develop, share, test, and document APIs. It is an application that is used for API testing. This blog aims to explore API testing automation using postman. Let’s jump right in,

Take your API testing automation to the next level with postman. Let’s talk.

An introduction to API automation

  • API automation determines if the application which is under test meets all the requirements for functionality, reliability, performance, and security.
  • It ensures consistent high quality as your application grows. 
  • Some critical component for automation testing APIs are the primary interface  to application logics. 
  • The most stable interface GUI tests are not sufficient to validate all functional paths of a multi-tier architecture. 

So, let’s understand by collections as that is the main part for the API testing. 

Import collection

  • File
  • Folder
  • Link
  • Raw text
  • Code repository

Scripts

Postman contains a powerful runtime based on Node.js that allows users to add dynamic behavior to request and collections. It also allows users to write test suits, test cases, and build requests that can contain dynamic parameters, pass data between requests, and more. Users can add JavaScript code to execute during two events in the flow, 

  • Pre-request script
  • Test script

Execution order of scripts

A pre-request script which is associated with a request will be executed before the request is sent. 

A test script associated with a request will execute after the request is sent. 

Let’s understand pre-request scripts through examples. 

Pre-request scripts

  • Pre-request scripts are nothing but snippets of code which are associated with a collection request that are executed before the request is sent. 
  • It can be added to a collection, a folder or a single request within a collection. 
  • These scripts run prior to each request in the respective collection or folder allowing for commonly used code to be executed prior to every request. 

Example of pre-request script from Postman

Test scripts

  • Test scripts confirm that API is working as expected. Integration between services are functioning reliably and that new developments haven’t broken any existing functionality. User can write test scripts for your postman API requests in JavaScript language. 
  • Users can add tests to individual requests to a collection of API or a folder in a collection. 
  • Postman includes code snippets so that user can add and then modify to suit test logic. 
  • Users can add however as many tests they need for each request. When users add tests to a folder or collection, they will execute after each request inside it. 

How to add test scripts in Postman?

  • In the Test tab from Postman request.
    • Example,

      pm.test(“Status code is 200”, function () {
      pm.response.to.have.status(200);});

  • Users can either write code in JavaScript or can add from snippets from the right menu option.
  •  This code uses the pm library to run the test method. The text string will appear in the test output. The function inside the test represents will appear in the test output. The function inside the test represents an assertion. Postman tests use the Chai Assertion Library (Which is an external JavaScript library used to write assertions. Compared to what we write directly in JavaScript, this assertion library needs less time and effort as well as easy use).

Chai assertions are BDD syntax, which provides options to optimize how readable your tests are to you and your collaborators. 

Assertions

The assertion checks whether the given prediction is true or false in any programming language. Assertions are nothing but code that can be used to check or analyze the response that is received from the server. 

Ways to add assertions in scripts, 

  • By testing the response body
  • By testing the status code
  • By testing headers
  • By testing cookies
  • By testing response times

Newman

Newman is a command line collection runner for Postman. It enables users to run and test a Postman collection directly from the command line. It’s built with extensibility in mind so that users can integrate it with continuous integration servers and build systems. Newman maintains feature parity with Postman and allows users to run collections the way they are executed inside the collection runner in Postman. Newman resides in the NPM registry and on GitHub. 

Set up Newman

  • Newman is built on Node.js, so Node.js must be installed. 
  • Install Newman using this command line.
    • $ npm install -g Newman
  • The easiest way to run Newman is to run it with a collection. 
    • $ Newman run mycollection.json
  • If your environment collection uses environment variables, provide an accompanying set of environment variables, export the templates from Postman and run them with -e flag.
    • Newman run {{json link of your collection}}

Reporting in Newman

This is how Newman’s report will be generated after this command.

$ Newman run mycollection.json

Now that you know how API testing automation with postman can create a great quality product, all you need is a trustworthy QA partner whom you can bank upon for all your testing needs. Zymr is a leading QA automation services provider that can help you develop rich quality software.

Zymr’s QA services for API testing automation with Postman

Achieve digital success in the disruptive business landscape with our technologically advanced, commercially viable, and economically feasible QA automation testing services. Take your digital services to the market faster, enhance your market coverage, and respond effectively to market feedback like never before. We have got you covered with all your API testing needs with the right tech stack. Let’s talk.

Contact our team to know more.Let’s talk.

Article Contributed by Meera Bagthaliya, Sr. Software Engineer – QE

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