API testing tutorial: How does it work?

Data Science   |   
Published December 4, 2020   |   

Making sure that your organization’s APIs are functioning properly is crucial both for ensuring the integrity of any apps or code you’re developing and for guaranteeing their functionality on launch. Let’s break down how API testing works and why you should prioritize it.

What is API Testing?

APIs (Application Programming Interfaces) are simply sets of protocols, tools, and scripting routines that help to connect an application to the Internet or other APIs. In other words, an API can tell one software program the best way to interact with a separate program or application, working as a digital bridge between two applications and facilitating efficient communication.
API testing, therefore, involves testing your API(s) regularly to check for any bugs, flaws, or inconsistencies. After all, if your API isn’t functioning correctly, you might accidentally think that there’s something wrong with one or the other applications that it tries to bridge.

How Do API Tests Work?

API testing usually works by gathering several excellent API testing tools (using multiple tools helps you cross-reference your results, and some API testing tools only perform specific tests or check for certain things) and using them continuously.
In fact, continuously testing your API(s) is crucial. At every step of your development process, new things between your application and your API might change. So it’s important to constantly run tests to catch any new bugs that may crop up as you move closer to your launch date.
Ultimately, it’s a good idea to run API testing to:

  • Make sure that your API functions properly
  • Make sure that your API can handle the load between your application and another, likely application
  • Make sure that your API works across operating systems, browsers, and more
  • See if there are unanticipated ways in which your future users could mess up the system

Benefits of API Testing

API testing can provide your website, application, or greater organization with a number of benefits.

  • For starters, API testing tells you quite quickly where any flaws or defects might be found in a system. Thus, you should be able to track down any bugs or glitches quickly and easily, minimizing the likelihood of a code-breaking bug later down the road
  • API testing tools (especially automated tools) can make it easy to run lots of tests repeatedly, minimizing the workload on your developers and ensuring that you have a steady stream of testing data coming in for analysis
  • API testing is also usually performed early (called “shifting testing left”), as you don’t have to wait until an entire application is developed. Therefore, API tests can also help you validate how well your greater application is responding
  • Lastly, API testing is just fast, especially compared to other coding tests. Some advanced API testing tools can run up to hundreds of tests in just a few minutes, helping you find more bugs in a shorter time frame

How to Perform API Tests

Fortunately, performing API tests is pretty easy so long as you have the right tools for the job.


To begin, you should set up an ideal API testing environment. Make sure that your parameters are set and that your servers and databases are configured based on what your tested applications require. Perform a standard API call to ensure that everything appears to be working smoothly before you start the real tests.

What to Test

You should try to cover a variety of potential trouble areas with your API tests. Here are some examples:

  • Usability testing involves checking whether your API is user-friendly and that it integrates with other platforms correctly
  • Discovery testing means checking to see if your API can list, create and delete certain resources
  • Security testing involves checking for types of authentication required and making sure that any sensitive data is properly encrypted

Don’t forget to use automated testing when possible and to thoroughly document any results. Some automated API testing tools can even automatically document their test results for further convenience.