In certain respects, an API is only as good as it is tested. For one thing, API testing is often an essential aspect of automation workflows. API testing tools let you automate many processes like making an API call and simulating stress. This makes API testing a critical component of automated systems like CI/CD.

API testing is also essential for ensuring API security and stability. It’s integral to getting your product to market and ensuring your users and customers get the best possible service. Finally, API testing is much faster and more efficient than other diagnostic tools. API tests are 35 times faster than UI testing, for example.

Considering its benefits, it’s unsurprising that API testing is discussed so often. But what kind of tests do they mean, though? API testing can refer to many different types of tests, depending on the circumstances. Below, we’ll review ten types of API testing. These will help you check everything from documentation and functionality to performance and security.

1. API Documentation Testing

API documentation is similar to a functional specification in UI testing. It ensures your API is set up how it should be. If there are any deviations from how an API is supposed to function, it will be documented in your event log. API documentation testing makes sure your API documentation is always up-to-date and correct.

2. Functional Testing

Functional testing is where you really begin to test your API’s functionality in earnest. It breaks down an API’s behavior into very small segments and then checks each piece. Happy path testing is generally included as part of the functional testing stage, as well. Functionality is the focus, though. Later testing stages will focus more extensively on output.

Functional testing can be broken down into three main components:

• Contract Testing: Contract testing is one type of functional testing. A contract’s primary role is to define the producer and the consumer. Contract testing makes sure that the producer and consumer are defined correctly.
• Component Testing: Component testing is the most extensive stage of functional testing. It makes sure that every HTTP transaction is valid. It begins by testing each request with both valid and invalid data. Then it measures the response status, response time, code, and message. These results are then compared against the expected outcomes to gauge your API’s performance.
• Scenario Testing: Scenario testing is similar to UI testing. It combines several functions into one interaction to see how your API will perform. A user authentication flow is one example of a series of actions that might be tested during scenario testing. Scenario testing lets you try authorized and unauthorized requests alike, giving you an overview of how your API will perform in every circumstance.

3. Integration Testing

Very few APIs operate in a vacuum. Integration testing ensures that all your APIs work together and that data is exchanged correctly. It’s also a valuable and efficient way to test your entire API ecosystem.

4. Performance Testing

Performance testing is another one of the most common API tests. It’s also one of the most important, as it’s how you measure your API’s performance in real time. Additionally, performance testing lets you emulate traffic spikes to help prevent unforeseen outages.

There are multiple components to a performance testing solution. Load testing, for example, measures how many calls an API can handle in a set amount of time. This leads to the next stage, stress testing, to measure how your API performs when it reaches capacity. Spike testing simulates the conditions of a surge in traffic to make sure your API can keep up. Finally, soak testing assesses how your API will hold up under heavy traffic for an extended period of time.

5. Regression Testing

Fixing or updating your API shouldn’t break it. That does happen sometimes, though, unfortunately. Regression testing ensures that your API is still functional after an update or fixing a bug.

6. Reliability Testing

Reliability testing makes sure that your API’s output is consistent and doing what it’s supposed to do. Reliability testing can also be a part of an integration testing system as it checks to make sure that the data being passed on to the following API is correct.

7. Runtime Error Detection

Ideally, you should be running runtime error detection during all of these API tests. Runtime error detection is a simple logging solution that records any errors that occur when an API is running. It’ll save you from having to go over your code line-by-line if something goes wrong.

8. Security Testing

Security testing is often the first thing that comes to mind when someone mentions API testing. That’s because it’s one of the most critical aspects of API testing, as it’s the only way to verify your API is secure from end to end and top to bottom. Security testing runs the user authorization flow in your API and ensures the right resources are delivered to the correct users. Security testing also checks to make sure your data encryption is correct.

There are a few different kinds of API security tests. A penetration test simulates an attack on your API to see how it will respond. Fuzz tests send random data and variables to your API, as well, to make sure there are no unexpected vulnerabilities.

9. Unit Testing

APIs are made up of a composite of smaller pieces. Unit testing lets you test each section of code, which is essential when analyzing a complicated API with many moving parts. Unit testing is more or less like debugging your API on a line-by-line basis.

Unit testing ensures that each component performs the way it should, assessing how each reacts to bad inputs or errors. Unit testing checks to see what happens when the state of the system changes. Finally, it analyzes what happens when the unit calls another function to see how everything works together.

10. Validation Testing

Validation testing is where you make sure your API is doing what it should. It’s conducted once you finish building your API. During validation testing, you’ll want to validate your schema and test your API is developed and built the way it’s supposed to be. Validation testing is also the stage where you begin to validate that your API does what it’s supposed to do.

Final Thoughts on API Testing

API testing is one of the most important aspects of maintaining a successful API. For instance, if you’re releasing your API for the first time, you don’t want to drop it on the marketplace and hope for the best. When you’re just starting out, service outages could be enough to sink your API before you even get out of the harbor. Even underperformance could be enough to make your users wary, depending on the competitiveness of your niche. If your API is bulky or bloated, users might jump ship to find a faster, more reliable product.

If you have a robust system with multiple API tests in place, you will know for certain how your API will perform in virtually any situation. API testing eliminates the formless anxiety and stress of worrying about what can go wrong and wasted effort fixing unexpected errors, so you can focus on making your API its absolute best and growing your company.