Before we get in to what Postman API testing is and how you can begin to use it, we first need to understand what an API is. API is an abbreviation for Application Programming Interface. It is a set of rules, which defines methods of communication. This aids various software components to interact with each other. API testing involves testing the collection of APIs to see if they meet return accurate response. The testing can determine whether it is well-structured and useful on basis of request parameter, the time taken.
What is Postman?
Postman is an application for testing APIs. It does this by sending a request to the web server and checking the response. This is a very useful tool if you are trying to understand REST APIs available or test the ones that you made. The user interface of Postman API testing is easy to understand even for a beginner, and you don’t even have to type in too much code.
Why Use Postman API testing?
Ease of Access
You can log into your account from anywhere, anytime as long as a Postman application is installed on the computer. This is an attractive feature to access files from various locations and collaborate with others.
Inbuilt organisation
To organised your test suites you can create collections with Postman. When this is coupled with sub folders and requests, it helps the user keep tab easily.
Specialized test creation:
The user has the autonomy to choose the test checkpoints. This is useful especially when you need to the test the API in one particular response.
Iterative testing
The options like Collection Runner or Newman enables the user to run tests in iterative loops. This saves time and effort by reducing redundancy.
Debugging
Postman makes it easy to debug APIs through testing. It is very transparent with the data received and its interpretation.
Installing Postman:
- Download the app from the Postman website.
2. Once it has been downloaded, double-click the installer and follow the prompts.
3. After the installation is over, launch the application by clicking the Postman icon.
4. When the application starts for the first time, users will be presented with a login window.
Understanding Postman API testing interface:
Postman provides several API call options (shown below) that can be used to test APIs of application. You can select API call method from the given drop down list, set Authorization, Header, Body information according to the selected call.
We can switch through the tabs to view the different information. For example, body information or header information. The blue send button on the right side, is used to send the request to the URL and receive response. The response can be saved using the send button next to it.
The process of testing API can be understood further through the following simple example. For this, we will use JSONPlaceholder. JSONPlaceholder is a simple fake REST API that is used exclusively for testing.
Example
JSONPlaceholder comes with the following resources.
| /posts | 100 posts |
| /comments | 500 comments |
| /albums | 100 albums |
| /photos | 5000 photos |
| /todos | 200 todos |
| /users | 10 users |
Of these, let us make use of the /users. We do this by typing https://jsonplaceholder.typicode.com/users into the URL tab
After this, click on the Send button to receive the response.
The response can be viewed in various formats which can be chosen from the following drop down list:
There are various kinds of tests that can be created in Postman. Feel free to explore the tool to understand the best fit for you.
Writing your own API test
First select the Tests tab, as shown below:
For this, let us use a open API available on GitHub https://hacker-news.firebaseio.com/v0/item/8863.json?print=pretty (copy and paste this into the URL tab). Then, type out the following test in JavaScript. This will check if the ID of the received object is the same as request ID(8863).
pm.test("Your test name", function () {
var jsonData = pm.response.json();
pm.expect(jsonData.id).to.eql(8863);
});After pasting the code and URL, send the request.
At the bottom tab, you can see that the test passed.
If you change the value 8863 to some other value or alphanumeric combination the test will not pass and will be displayed as a fail.
This is just the tip of the Postman and API testing iceberg. With this introduction and basic understanding, you can now begin to explore the plethora of opportunities and the possibility for much more advanced testing. If you have built and API and want to test it, go ahead! If you just want to explore the possibilities, use one of the public APIs available to expand your horizons!
