What is API Testing? (+Types and Best Practices)

APIs are crucial for communicating between software systems. Hence, API testing is essential to ensure they function, provide security, and perform well.

As a developer, you usually conduct it at the end of your development, but it is best done earlier using a shift-left approach. 

This enables you to get faster issue resolution, and here we discuss what API testing involves, the types of API testing, advantages, and best practices you can follow.

What is API Testing?

API (Application Programming Interfaces) verification is an essential process that helps ensure an API's performance, functionality, and security.

It involves different test types, each designed to maintain API reliability. Developers can execute API tests manually or automatically using special API testing tools.

Usually, API testing is conducted after the software development cycle. However, more people are adopting a testing approach known as shifting left these days. 

With this strategy, you get a fast iteration that enables you and your team to identify and resolve issues as they arise. Great. Now that we have answered what API testing is, why is it important?

Why is API Testing Necessary?

API testing offers you many benefits as a developer, end-user, and tester.

Efficient Back-End Testing

A user interface test cannot always validate API services' functionality and does not cover all the critical aspects of backend testing. With the test, you can identify and fix bugs at the server, unit, or level, which can delay a product’s release that needs extensive code rewrites.

Early Testing Detects Problems Faster

You can start testing early in your SDLC before the user interface is ready.

This allows you to quickly catch bugs and fix them at the server layer before they become visible at the UI layer, helping to prevent them from becoming a bigger problem.

For example, you can make unadvisable requests through the UI, which exposes security flaws.

Creates an Infrastructure For Microservices

API testing is becoming crucial, mainly if you use microservices in your applications. It ensures that all parts of your software work. Each section of an app has separate data stores, and different commands interact with them using APIs.

Enables an Agile Software Development

For agile software development, API testing requires instant feedback on your process flow.

In an agile environment, API and unit tests are better than graphical user interface (GUI) tests as they are efficient and easier to maintain.

GUI testing needs extensive reworking to keep up to speed with the rapid environmental changes.

Types of API Testing

1. Performance Testing

Performance testing is often neglected but crucial for identifying issues under load. This can lead to performance discrepancies compared to production testing environments containing less data.

Your testing must consider traffic spikes and heavy processes. Hence, your testing environment must closely mirror your production environment for the best results.

2. Unit Testing

You must write automated tests to run with every application built for unit testing. The tests integrate with your codebase and must consistently pass during the builds.

These codes for API hinge on the risks and functionalities associated with them. You need a strong foundation for effective unit testing that influences subsequent testing phases.

3. Load Testing

Load testing works hand in hand with performance testing, but it focuses more on simulating a steady stream of traffic instead of spikes.

This approach helps you identify memory leaks and other flaws that can arise from lengthy usage.

It is essential that the APIs can handle supported loads to maintain operational stability.

4. Integration Testing 

APIs are essential in systems that facilitate and integrate various system elements.

You must thoroughly test to ensure the APIs process incoming and outgoing parameters correctly, adhering to the defined constraints.

Furthermore, you must implement a powerful sanitization of the incoming traffic to help maintain your system's integrity.

5. Security Testing

Security tests are necessary but mostly underfunded. You need a thorough risk analysis to be conducted by professionals to help avoid oversight.

As a developer, you must adopt a security testing mindset as your APIs serve as essential entry points for the infrastructure.

It is usually referred to as pen testing (or penetration testing.) It should evaluate the API entry points, legacy APIs, and data flow.

6. Runtime Error Detection

Throughout your testing phase, runtime error directions are essential. It allows the APIs to report any defects encountered in the operation to facilitate a timely redemption.

7. Fuzz Testing 

This is the final validation step before you deploy your application. It involves transmitting random data to the API endpoints, focussing on server behavior.

Runtime error directions are essential throughout your testing phase. They allow the APIs to report any defects encountered in the operation, facilitating a timely redemption.

The APIs must handle any unexpected inputs without crashing or exhibiting unpredictable behavior. Fuzz testing can be more exploratory or structured depending on the risk assessment.

8. Interoperability Testing 

For interoperability using third-party services or legacy systems, you need careful planning.

Your test plan must outline your testing strategy, including the severity and priority of any potential defects based on your historical data.

Using the approach will inform you how API testing is done during interactions with other external systems.

9. Validation Testing 

Confirming that your software meets your business requirements is vital during validation testing. You must evaluate if the execution results align with your expectations outlined in a test plan.

It also facilitates UAT (User Acceptance Testing), which guides stakeholders through different scenarios and documents any deviations from expected outcomes. Business users' approval will signify readiness for deployment.

Advantages of Using API Testing

You Get Improved Test Coverage

API testing automation gives you a thorough test by validating various endpoints, response codes, and request methods.

Validation testing is vital for confirming that your software meets your business requirements. You must also evaluate whether the execution results align with your expectations outlined in a test plan.

Testing different scenarios helps identify vulnerabilities and ensure compliance with requirements, ultimately enhancing API reliability and security for real-world applications.

Reduced Shift-Left Strategy

API testing is quick to implement because it does not rely on GUI. You can adopt a shift-left strategy, enabling you to run tests early in the development cycle. This results in immediate feedback and the ability to address issues sooner, with tests typically completed in seconds to minutes.

Faster Bug Identification and Fixing

API automation testing detects bugs early in the development lifecycle, decreasing the time spent fixing problems. Addressing issues at the start can avoid expensive rework and enhance the quality of your product.

Saves Costs

With API testing, you can cut costs on repetitive tasks and reduce manual effort using automation. Continuous tests help optimize resources while lowering expenses during early bug detection, providing a streamlined process that enhances ROI.

You Get Enhanced Scalability

As your organization grows, your API needs increase with user demand. With API testing, you can do high traffic and stress tests to help identify scalability issues. When you address these early, it ensures a smoother user experience and avoids disruptions.

Helps Speed Up Software Development

API testing can quickly speed up software development, reducing the time needed to go to market. It also allows you to run automated tests quickly and repeatedly, helping your teams detect and fix problems early.

API Testing Challenges

Aligning the specific requirements to sequence API calls is a crucial step that requires time and effort. To minimize manual time, it helps identify, validate, and automate challenging tests.

Hence, assessing system integration for APIs will require concentrated effort. You must emphasize the API design to help evaluate performance and responses and ensure that the API call functions.

Therefore, you must track the impact of the ARI test automation framework when changes occur, such as adding new features or enhancements.

You must validate the API parameters to establish the necessary checkpoints to mitigate important security and stability issues.

Lastly, when updating the API test schema, you must revise it with each update to maintain it throughout your testing lifecycle as it defines the grammar and syntax of your test documents.

API Testing Tool Essential Features

An effective API tool must include essential features to help enhance your testing for smooth and accurate results.

• It must support multiple protocols such as REST, HTTP, and SOAP.
• Designed with built-in test management, providing you with a centralized platform to create and execute test cases.
• You need automated testing capabilities to execute test cases without having to do it manually.
• Another essential feature is request/response validation, which supports the JSON/XML schema and verifies that the data adheres to your predefined schema.
• Having mocking and virtualization functions can help isolate tests. You can create mock endpoints that replicate the behavior of the APIs, and virtualization helps extend the simulating response using third-party APIs or a backend system.
• Lastly, it helps with performance testing and scalability, like testing load stress, and provides you with performance analytics.

API Testing Best Practices

When you adhere to some best practices, you can ensure you have a smooth and reliable testing process:

1. Always test your development cycle as early as possible to help identify potential issues.
2. Use automation to help leverage and streamline your testing process instead of doing it manually.
3. Implement assertions to help validate your expected API outputs. These include measuring response times and structuring the analysis of the response data.
4. Test all the API endpoints to ensure they are functioning and test the chaining of requests to help verify the integrity of the data flow.
5. Conduct your security tests to ensure the API safeguards your sensitive information.
6. Measure the API performance when under heavy loads to guarantee it can handle large volumes of data.
7. Evaluate and test usability and compatibility to ensure it is intuitive and easy to implement on various platforms and other devices.
8. Monitor the tests continuously and update them as needed while performing a regression test to ensure that your updates or fixes do not introduce new problems.

Wrap-Up: What is API Testing?

API testing ensures that software functions well and is secure. Using the shift-left strategy, you can detect and resolve problems as early as possible to enhance the quality of your products.

Adapting and utilizing your testing tool's best practices will improve and ensure thorough test coverage. As APIs become essential to applications, a robust API testing tool is vital for delivering reliable, secure software solutions.