APIs come in many different shapes and sizes and have been around for a long time. Whether you are brand new to the topic or think about your day-to-day in terms of RESTful methods, you are using APIs every day.
"This morning I PUT on my clothes, went to the kitchen to GET a cup of coffee, sat at my computer and felt the satisfaction of finding emails to DELETE that don't need any action from me. My morning ended up being pretty 200 OK."
Any developer will tell you that testing is a very important part of creating world-class software. They will also tell you that they were on a tight deadline and they had to skip writing tests. But don't worry, their code is "rock solid". In this post we'll start with the definition of an API and walk through some reasons you should test your APIs. Then we'll talk about why it's important to test your APIs and share some tips on how to use modern tools to help automate the process.
Let's dive in!
Definition of API
An API, Application Programming Interface, is like a waiter who takes orders from one application and delivers it to another. It's the backbone of many modern software applications, connecting various components to ensure that everything runs smoothly. But like a waiter, APIs can sometimes make mistakes, which is why it's important to test them thoroughly.
What is API Testing?
When it comes to ensuring optimum performance of APIs, testing is undoubtedly essential. It involves verifying not only functionality but also the API’s security levels and ability to perform well under pressure. Thorough API tests entails sending requests to an endpoint followed by analyzing its respective response(s). The results confirm if indeed the API operates in compliance with specific requirements; returns predicted information while also managing errors efficiently.
A good friend of mine stole a quote from a famous philosopher and loves to use it whenever we are talking about how to ensure the quality of the software we are creating:
"Quality is not an act, it’s a habit" – Aristotle
This starts with solid requirements and extends through the creation of automated testing of your software. APIs are no exception, in fact, they are probably more important to test since the primary consumer of your APIs will be other developers who depend on the stability of your application.
Long gone are the days where manual testing was the primary method for ensuring code quality. Automated testing now rules the landscape and building your tests into deployment pipelines will save a lot of time (which business leaders also call "money") and free you up to work on new, exciting applications rather than an endless queue of bugs to fix. It's not a silver bullet to solve all quality issues but the more you automate the easier your life will be.
Some popular tools for API testing include Insomnia, Postman, SoapUI, and Selenium. These tools allow you to test your API endpoints, automate your testing process, and generate reports to help you analyze your results.
So, whether you’re creating a new application, managing an existing application, or keeping the lights on for a legacy application, testing your API is essential.
The holy grail of any API is to be so intuitive that no documentation is needed. Unfortunately, Indiana Jones isn't available for most developers so the Holy Grail remains elusive so we need to make sure all of our APIs are well documented. This includes both internal and external APIs.
Documenting your API is crucial because it helps other developers understand how to use it effectively. It provides information on the different endpoints, input parameters, response formats, error messages, and API authentication requirements. By providing clear documentation, you enable other developers to integrate your API into their applications more quickly and with fewer errors. Well documented APIs can also help reduce the number of support requests you receive from developers who are struggling to use them.
Types of API Testing
Just like our waiter friend that is delivering food from the kitchen to our table, there are many different things that can happen by mistake. Your food could take too long to get to your table and be cold ("meal latency"), someone else could get food meant for you ("meal-in-the-middle attack"). So there are many approaches that you can take to ensure your APIs are doing what they are supposed to do at scale and are as protected as possible from bad actors.
Does the code do what it's supposed to do? This is where robust requirements and techniques like Test Driven Development (TDD) are your friend. As a developer, you can only test for what you are told the software is supposed to achieve. Functional testing should be straightforward given good requirements and will save a lot of time and headaches down the road when someone else has taken over your code.
The importance of securing your APIs is becoming more and more important as businesses adopt widespread use of APIs to exchange data both internally within the business and externally to partners and customers.
A key component to any well designed API is low latency. Oftentimes APIs are just one part of the overall process that perform some higher-level business function. The chain of logic is oftentimes extremely complex and any weak links are often difficult to find when performance suffers. Making sure you are aware of your APIs performance metrics and tracking any fluctuations based on changes made behind the scenes will help you quickly and efficiently identify where bottlenecks are occurring. This can also be affected by any upstream APIs that your application is using so try to separate the latency within your application as well as any latency that could be caused by external systems.
Integration testing is the process of testing how different components of an API work together to ensure they are functioning correctly. It involves testing the API’s input and output as well as how it integrates with other components within the system. This is an often overlooked testing technique when developing APIs. Since your application is most likely relying on the APIs of other systems, it is critical that you know when they are unavailable or have changed in a way that you are not anticipating. I recommend that you set up tests (and alerts) on any external APIs that are part of your critical business workflows.
Since most APIs are called by external applications, you don't have control over how and when your APIs will be used. This means your application is exposed to malicious attacks, bugs in code that hit your APIs more than they should, and don't forget what happens when your APIs become really popular and more applications need to access them.
API Automation Testing
Automated testing is a great way to speed up the testing process, especially for regression testing and load testing. You can create automated tests that run every time you make changes to your API, ensuring that you catch any issues early on. They can be built into your CI/CD pipelines or run locally to make sure new changes don't have unintended consequences.
Test Automation Tools
I've already mentioned the importance of adopting automation into your API process. There are many tools on the market for API testing including Insomnia, SoapUI, Postman, Grafana's K6 and Selenium. These tools allow you to test your API endpoints, automate your testing process, and generate reports to help you analyze your results.
API testing is an important part of the software development process. By testing APIs thoroughly, developers can help to ensure that their APIs are working correctly, secure, and performant. There are a number of different ways to test APIs, including manual testing and automated testing. Automated testing can help to speed up the testing process and improve the accuracy of the tests.