What Is API Testing and Why Is It Important?

Debra Hopper
February 17, 2023
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APIs share data and enable communication between everything connected to the internet. API testing ensures that these connections work as intended and that the information carried by APIs remains secure.

What is API testing?

API testing is a type of software testing that tests application programming interfaces (APIs). API testing helps developers identify bugs within the API and optimize its performance, functionality, reliability, and security. 

What is an API?

API stands for application programming interface. APIs share data and enable communication between different applications and software systems within set parameters. 

APIs connect and carry information between everything connected to the internet, from your smartphone to your car. Many everyday digital actions include the use of APIs, from checking the weather within your weather app to making purchases. Any time you ask one application or website to call information from another website, it is an API that pulls that information. 

One example of an API at work is when you “log in with Google” or “log in with Facebook” to an outside website. An API provides information to identify you to the website without giving it your Google log-in information. 

Similarly, it is APIs that allow you to pay for online purchases with third-party payment methods like PayPal. When you “pay with PayPal”, an API communicates your user information, the amount owed, and confirms your purchase with PayPal and communicates back to the site you're buying from that you’ve paid.        


Why API Testing Is Important

Api testing is critical to ensure that connections between platforms are reliable, safe, and scalable. API testing validates that the API performs as expected, and, more importantly, doesn’t act in unexpected ways that may increase the risk of an exploit. 

API testing is especially important because if an API breaks due to undetected errors, you run the risk of not only breaking your app, but an entire chain of software that uses it. Undetected API errors create bad user experience across the software chain and open the door for malicious actors to gain access to sensitive data carried by the API.

API testing checks for bugs such as duplicate functionality, improper messages, incompatible error handling, and security, reliability, and performance issues. API testing involves running multiple types of tests which check for different issues, including:

Validation testing 

Validation testing checks that the API behaves as expected and runs efficiently. 

Functional testing 

Functional testing ensures that the API returns the right response for a given request and makes sure that it handles certain scenarios well within the planned parameters.

Reliability testing 

Reliability testing ensures the API produces consistent test results and can be connected to consistently. 

Load testing 

Load testing measures how many calls an API can handle and monitors the API’s performance at expected normal and peak conditions. 

Security testing 

Security testing checks that the API is secure against external threats. Security testing methods include fuzz testing and penetration testing. Security testing also includes steps like validation of encryption methodologies and API access control.

Runtime and error detection testing

This type of testing evaluates the actual running of the API, focusing on monitoring, execution errors, resource leaks, or error detection


Benefits of API Testing

Overall, investing time into API testing is beneficial for both development teams and their customers. API testing creates a better user experience and improves software security. 

Improved Reliability and Customer Satisfaction

By identifying any flaws or bugs in an API before it goes live, teams can provide a better experience for their users from day one and reduce unexpected downtime which could otherwise have a negative impact on customer experience. 

Improved Security

API security testing is especially important because of the increasingly important user data carried by APIs. API testing can reveal vulnerabilities in the application’s architecture, allowing development teams to fix them before malicious actors can exploit them and gain access to sensitive data. 

When should you API test?

API testing should begin early in the development cycle and be conducted as a continuous process throughout development. By testing APIs throughout the development process, teams can ensure that what they’re building works as intended and is of a high quality. This method of testing software earlier in the development cycle is known as shifting left.

When API testing is shifted left, the benefits are even greater, saving developers time and money. The benefits of early API testing include:

Ship Software Faster 

Having automated tests in place early on allows teams to quickly identify what needs to be addressed or changed in the API and perform fixes before code is released to production.This helps to speed up development cycles.

Time may also be saved in the future by testing APIs regularly and ensuring they are able to scale effectively as usage increases and new features are added over time. 

Reduce Costs

Early API testing allows teams to fix bugs before they become serious problems. The earlier in the process an error is found, the less expensive and more quickly it is able to be dealt with. If issues can be fixed before UI testing begins, they won’t affect production, so conducting API testing early saves development teams money in the long run. 


Mayhem for API Testing

The easiest way to conduct API testing throughout the development process is by using an automated API testing tool like Mayhem. Mayhem automatically creates test cases and integrates seamlessly into your continuous integration pipelines, making it easy to conduct API testing at speed and scale. 


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