APIs have become essential for building high-quality software, enabling different components and applications to communicate with each other and share data. In fact, most business logic is now handled at the API layer, making them an important factor in delivering high-quality user experiences.

In this guide, we’ll cover what API testing is and why it’s important for improving customer experiences. We’ll also discuss ways to implement automated API testing that deliver better results than traditional methods.

What Is API Testing?

API testing is a subset of software testing that focuses on an application programming interface's (API) functional and non-functional performance. This involves going beyond the graphical user interface (GUI) of an application, and directly testing the underlying business logic implemented at the API layer.

Since most modern applications use APIs for internal communication between components or externally with third-party services, they’re an important aspect of software quality. In fact, the State of Testing in DevOps Report found that automated API testing is one of the most impactful tools testers have to improve customer happiness.

The Different Types of API Testing

A comprehensive testing strategy requires many different testing methods to validate an API for functionality, reliability, performance, and security. By implementing a variety of test types, quality teams can ensure the APIs and applications they’re responsible for meeting the organization’s standards before deployment.

Here are the most common types of API testing methods:

  • API Unit Testing: Assessing individual sections of API code in isolation. This involves evaluating functions, methods, and other small code blocks to ensure it behaves as expected.
  • API Integration Testing: Analyzing how the API interacts with other APIs and application components. These tests can check how well the API integrates with different systems, platforms, and software.
  • API Functional Testing: Verifying the API behaves as expected based on its contract or specification. An API specification could include endpoint availability, acceptable inputs, expected outputs, and desired behavior under various conditions.
  • API Load Testing: Evaluating API performance with various real-world workloads. This involves simulating a high volume of API requests to analyze response times, throughput, and other performance metrics.
  • API End-to-End Testing: Validating the entire flow of an API endpoint, including multiple API calls, database transactions, and interactions with external systems. This brings together functional testing, integration testing, and more to evaluate an entire API flow.
  • API Regression Testing: Ensuring new changes to the API do not break existing functionality or introduce unintended side effects. This involves retesting other aspects of the API to verify they still work as expected.
  • API Security Testing: Identifying potential vulnerabilities in the API code that could pose a security risk. This includes authentication and authorization flaws, data integrity issues, and more.

Overcoming the Challenges of Traditional API Testing Methods

When most software teams implement API testing, they often turn to a traditional tool or API testing framework like Postman, SoapUI, or REST Assured. These traditional tools usually require coding experience and fail to take into account the full user experience. This makes them an efficient way for developers to quickly validate code changes, but less useful for a more comprehensive API testing strategy.

When only technical team members can contribute to testing, this leads to a bottleneck that slows down the overall testing process. A low-code testing approach allows any team member to create and manage tests, regardless of coding experience. This means adopting a low-code API testing tool can enable organizations to scale their test suites and achieve better coverage. 

In addition to low-code tools, combining API tests with UI tests in the same test suite is more impactful than only using standalone API tests. Extending the coverage of end-to-end tests to APIs can better evaluate user flows that directly rely on APIs because these tests ensure the front-end and back-end work together seamlessly.

Executing API tests alongside UI tests can also accelerate the testing process. Since API tests do not need to interact with the browser, they can be executed within seconds rather than minutes. This can reduce the time required for end-to-end testing at later stages of development and lead to faster delivery cycles without compromising on quality.

Low-code API testing solutions shorten the test creation process by supporting migrations from API management platforms like Postman. A Postman integration makes it easy for teams to use existing API test collections and run them with UI tests.

Best Practices for Implementing Automated API Tests

While UI tests are slower and often implemented during the later stages of development, API testing is faster and can be integrated much earlier in the DevOps pipeline. For example, running unit and integration tests during the coding stage helps software teams identify and resolve API issues before they even push code.

API load testing typically is implemented later in the development process since it requires environments that as closely as possible resemble the production environment. However, teams have been evaluating changes in performance as early as the coding phase - by ensuring that earlier environments are consistent and setting a baseline measurement as a guide to detecting deviations.

This approach can catch performance issues early when they're easiest (and cheapest) to resolve. Automated security testing can be integrated throughout the development process, but some techniques like penetration testing are usually performed closer to a software release.

When writing the API tests themselves, it’s important to strike a balance between API unit tests and end-to-end API tests. Integrated API tests are useful for accelerating end-to-end tests that are taking longer to execute and increasing test coverage of some user flows. At the same time, standalone API tests are a great way to start shifting testing to the left. Or, you can use them to verify the quality of public APIs that your customers rely on for their businesses.

Low-Code API Testing with Mabl

Mabl is a low-code test automation platform that enables quality teams to integrate API testing into their end-to-end tests to accelerate development cycles and expand test coverage. Using our intuitive UI, anyone on your team is empowered to expand your automated test suite to include APIs. This unifies UI and API testing into a single test automation platform that provides comprehensive performance insights for your application.

If developers are already relying on a traditional tool like Postman to manage APIs, importing Postman Collections directly into mabl allows them to get started creating API tests quickly. This enables development teams to take advantage of mabl’s test orchestration and unlimited test runs. API tests can also be leveraged to develop API load tests, too.

Ready to adopt automated API testing? Claim your free 14 day trial with mabl and start building an integrated API testing strategy with low-code test automation today.