How to Use Postman for API Testing - A Complete Guide

API is an important aspect of the software development process, where it enables data exchanges between multiple software components. API functionalities of software can be tested using many tools, and Postman is one of them.

This is widely popular among software testers, and they use it to basically understand if the systems or software is performing appropriately. Here I will talk more about the Postman for API testing and know its basic features.

What is Postman for API Testing?

Postman falls under the category of a comprehensive API testing tool that developers use to create, share, and document other APIs easily. As far as I can remember, Postman was developed to be a simple extension of Chrome. But now it has really evolved into a massive application that is available for use on multiple platforms. Some examples I can provide are Windows, macOS, and also Linux.

Why Use Postman for API Testing?

There are several reasons that make it essential to use Postman for API testing as one of the go-to tools. Here let me explain some reasons why, from my perspective, I found it useful:

1. Ease of Use: Postman provides their users with an easy-to-use interface, which makes it possible for a user to get started in API testing using Postman. Moreover, you are also getting the potential to automate tests and also include minimal hassle and there is no need for scripting. Such an intuitive platform makes working using the platform a breeze. This is even for people who have minimal experience with scripting.

2. Lots of Available Features: You can find that there are a lot of available features in the system and it helps you test components easily. You can easily perform tests like environment management, automated testing, and integrate collaboration tools, etc. You will also be able to access some of the authentication tools on the platform like OAuth, API Keys and JWT. Thus, with the availability of features and support authorization, you can easily test APIs without complex security parameters.

3. Cross-Platform Availability: API testing Postman is usable in both ways, that is either as a standalone application or it is available on multiple application systems. I would also recommend you try out its web version, which is directly usable from your browser. Therefore, whatever the type of platform you may be using, integrating Postman’s API testing feature is not difficult.

4. Collaboration: Postman helps you to share your API requests, collections, and environments directly with your team. I have personally found this feature useful as during environment testing having only self-opinion downgrades the software development lifecycle. You will require a collaborative environment when the API testing with Postman is in progress; there is no shortcut to it.

5. Automation of Continuous Integration and Continuous Deployment (CI/CD): If you are familiar with DevOps then CI/CD protocols are no longer new to you; Postman supports the process.  The API tester is known to allow running the tests as a part of the CI/CD pipeline. There are several tools like Newman, Postman’s command-line companion which helps in executing Postman tests across various environments.

6. API Documentation: Postman API serves as a great way to generate and share API documentation. It can be used as a collaboration tool and it ensures the stakeholders are accessing the up-to-date information regarding the APIs.

How to Test API Using Postman?

Several of the steps are involved with Postman for API testing, and it is essential to understand the steps. We will start by understanding setting up requests and end by running an automated test.

1. Setting Up Postman: Initially, it is essential to note that you need to download and install Postman from the official website of its distribution. If you do not have an account, consider opening one for free. This account will be your one-spot location to sync your work across various platforms.

2. Creating First Request: If you need to test the API we will start by making the steps in order to create the request. The steps that you might use are as shown in the section below:

Step 1: Click on the ‘New button’ on the Postman interface and select ‘Request’.

Step 2: You will be asked to name your request and choose the ‘Collection’ (store) where you want to save it.

Step 3: In the request builder you need to now enter the API's endpoint URL in the address bar. Suppose you are running a weather-checking API, then your link might look like this:

https://api.weather.com/v3/weather/conditions (it as the API key generator is absent, it is just an example).

Step 4: After that, kindly select the HTTP (HyperText Transfer Protocol) method. This is expected to include (GET, POST, PUT, DELETE, etc.) from the dropdown menu.

Step 5: The next step is that you need to enter the query parameters and then a header to distinguish it apart from the other projects running.

Step 6: After that you need to click on “send” and then execute your request. This is how you can start generating your first own request in the Postman for API testing tool. Next, the postman will display the response from the server in the lower panel. After that, you can review the status code, headers and body of the response from the lower panel.

3. Organizing Requests with Collections: With the usage of Postman, you can easily create API requests and collections which can be accessible via the user interface of Postman. These collections are a group of requests that help to manage chunks together and help you to track the tests easily.

Now let us help you out with creating the collections for the test as well. This we will deal with in the section situated below:

Step 1: Click on the ‘collections’ on the left-hand side of your screen. Now you need to select the ‘New Collection’ subsequently. Name your collection and add a description if required, you may skip this for the time being.

Step 2: After creating a collection, you can save it to collections by clicking on the ‘Save’ button. Select the desired location where you may need to save it.

Step 3: Within the collection, you may create folders and organize your requests further. For example, you may have folders for different API modules, such as “User management” or “payment processing”, etc.

4. Using Environment and Variables: The environment in API testing with Postman allows you to manage different sets of variables that can be used across requests. This is going to be particularly useful if you are trying to test an API under multiple environments which includes, development, staging, and finally the phase of production.

• Creating the environment: To create the environment, you need to visit the ‘Environments’, tab and click on ‘Add’. I would suggest you define variables like, {{base_url}}, or {{api_key}}.
• Switching Environments: Once you have developed an environment, the next stage is switching between them using drop-down.
• Using Variables: When you create the requests kindly use the variables under the double parenthesis, like “{{variable_name}}”. Now the Postman API will automatically replace the placeholders with corresponding values which are selected from specific environments.

5. Writing and Running Tests: Postman for API testing simply allows you to run and write tests in JavaScript. These are executed after you have sent an API request. Using such tests, you can easily validate the response status, body content, headers and more.

1. Writing Basic Tests: To write a test, go to the ‘Tests’ tab inside the request builder. I will provide a simple example to check the response status code for a function is 200 and return affirmation:

2. Advanced Testing: You can even write some complex tests to validate specific aspects of the response. Take this code as an example, to check ‘user.id’ field in JSON response is equal to 1:

3. Running Tests: After you have written the tests, finally click on “Send”. This will enable execution of the test queries, and the results will be displayed in the ‘Test Results’ section.

6. Automating Tests With Collection Runner: The collection runner is exclusively known as one of the powerful features that is available in Postman for API testing. It allows you to run requests, in the collection along with the associated tests. Such testing features are especially useful for running data-driven tests, or regression tests.

1. Running Collections: Click on the “Runner” button and select the collection that you want to run, configure their iterations, and click “Start Run”.

2. Data Driven Testing: With the usage of Postman, you can support your tests in a data-driven format as the files that you can upload are a CSV or a JSON file. These files contain all the test data and complete the tests for each of the rows of data and substitute the variables accordingly.

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Top Practices for API Testing Using Postman

Postman is a great tool which requires sticking strictly to best practices while a person uses it. I will help you get to know some tips and tricks that are particularly responsible for getting the most of the benefits out of the Postman API testing:

● Please make sure that you make collections and folders for organizing the requests in a serial manner. As your API grows in complexity the collections and folders help to maintain the entire tests properly.

● The usage of the Postman’s environment helps in avoiding hardcoding of the features and values that are present in your requests. Thus you are able to make your test regimes easier and maintain added flexibility.

● Always try to write tests that are reusable for many such application developments. Like if several endpoints return a status code of 200 when successful, create a reusable test that checks for this.

● Automate your tests using Collection Runner and Newman, and integrate Postman in your CI/CD pipeline. Ensure that your APIs are tested automatically, every time there is a slight change in the code.

● Use Postman’s documentation features to generate and share the API documentation. It helps your team and even stakeholders to have access to up-to-date API information.

Conclusion

The usage of Postman for API testing is one of the powerful and versatile tools that helps in having an intuitive interface. It also helps in getting greater automation capabilities for the people. With such features, you can be sure Postman API is going to be one of the most popular set of tools for software developers.

Start following the best practices and make sure to play on the maximizing effectiveness of the tools. Using the Postman API will let you understand that it is one of the best tools and that it is indispensable in maximizing effectiveness at the same time.

If you need more information regarding the software development and gather hands-on training then kindly join the automation testing course. At StarAgile, we are responsive and effective in providing you with the best automation testing courses from our side.

Also Read: When to Use Automation Testing?

FAQs

1. Is Postman enough for API testing?

Yes, Postman for API testing is a superior and exclusively great option for different testing scenarios. This API tester is known to exclusively support a wide range of functionality checks and helps in authentication. Apart from that, it also helps in performance testing, and automated regression testing. However, if you are trying performance testing or load testing, I would recommend integrating Postman with other specialized tools like JMeter or LoadRunner.

2. How many days to learn Postman API testing?

The time it takes to learn Postman for API testing depends on your prior experience with APIs and testing tools. Provided you are new to API testing, it might take you around a week to get comfortable with the basics. Some of the basics also include sending requests, understanding responses, and writing simple tests, etc.

3. Is Postman a good API?

Please know that Postman is not an API itself, but an excellent tool for testing and interacting with APIs. Postman allows you to do a load of functionality in regards to testing and see the other APIs and their functionality effectively.