API Test Automation: What It Is and Best Practices Guide

API Test Automation: Definition and Best Practices

Software testing is vital regardless of the type of software you write, but it’s certainly even more crucial when it comes to software that’s consumed by third-party code. That’s why API testing is so relevant in today’s world it has become common practice that applications are developed following the “API first” methodology. In this post we bring you an introduction to API test automation.

We’ll start by reviewing APIs. This term has unfortunately become a bit loaded, so it’s crucial we define it well. After we’re all on the same page, we’ll cover API test automation itself. You’ll learn the fundamentals of API test automation, including definition and benefits, and the best practices you must be aware of.

Let’s dig in.

Understanding APIs

API is one of those terms that might mean several different things, in different contexts. But nowadays, most of the time when someone says “API,” they mean one specific type of API. To clarify all of that, we’ll open by reviewing APIs.

What are APIs?

API stands for application programming interface. In the most general sense, it means any kind of interface, or contract, that allows one software program to be used by another one. A piece of software that exposes an API will offer routines or services that another application can call in order to benefit from that functionality.

For instance, if you have a class that’s meant to be used by a third party, the collection of public members from that class is its API, or interface.

This is probably the most striking difference between an API and a “normal” software program: while the latter is intended for human usage, the former is targeted at other pieces of software.

Types of APIs

We’ll now briefly review some of the main types of APIs, with definitions and examples.

Libraries and frameworks – Reusable code packages that solve common problems

• Polly (.NET library for retry policies)
• Django (Python web MVC framework)
• Jest (Node.js unit testing library)

Operating system APIs – Interfaces for applications to interact with system resources

• Win32 API (Windows)
• POSIX APIs (Unix systems)
• DirectX (Windows graphics and game programming)

Hardware APIs – Protocols and interfaces for hardware-software communication

• Device drivers
• USB protocols
• Graphics card APIs (DirectX, OpenGL)

Database APIs – Interfaces for applications to interact with databases

• JDBC (Java Database Connectivity)
• ODBC (Open Database Connectivity)
• MongoDB API

Web APIs – Interfaces for applications to communicate over the internet

• REST APIs (HTTP-based interfaces following REST principles)
• GraphQL (Query language for APIs)
• SOAP (XML-based protocol for web services)
• WebSocket APIs (for real-time bidirectional communication)

The list above isn’t exhaustive, but it’s enough to give you an overview of what’s out there when it comes to API types. What’s crucial to understand is that nowadays when most people say “API” they actually mean “web API.” And even more specifically, they probably mean a REST API.

So, for the remainder of this post, that’s the kind of API we’ll be talking about.

Role of APIs in Modern Software Development

Modern software is a complex and diverse field. We can, however, pinpoint a few general properties that help us understand the role APIs play in it.

• Modern software development is often distributed. Instead of a single monolithic application, you’ll have many microservices that need to communicate with each other, and often do it via APIs.
• Integrations play a big role in today’s software development. It’s extremely common to rely on a number of third-party services, and communication with such services will often happen via their web APIs.
• Modern software needs to run on a variety of devices. Applications today need to be available for Windows, Mac OS, web, Android, and iOS. To ensure consistent behavior and reduce code duplication, it’s common for those frontends to use a single API under the hood—or even multiple APIs, if you choose to use a pattern like BFF (Backend For Frontend)

To summarize: modern software applications are integrated, distributed, and run everywhere, and APIs play a big role in enabling all of that flexibility.

Fundamentals of API Test Automation

Now that we’re on the same page regarding APIs, their definition and importance, let’s talk about API test automation.

What is API test automation?

API test automation is the practice of automated testing, applied to APIs. With API test automation, you’ll have a suite of automated tests that make requests to your API and compare the results with a set of expected values. Those tests can be executed on a certain schedule (e.g., nightly), but the modern practice is to add them to your CI/CD pipeline, so they execute every time a developer pushes their commits to the main branch.

With test automation, you can run a huge number of test cases in a fraction of the time it would take human testers do to the same.

What are the benefits of API test automation?

The benefits of API test automation are essentially the same as other types of software test automation. With test automation, you can run a huge number of test cases in a fraction of the time it would take human testers to manually do the same. Also, this ensures to substantially higher degree that tests cases will execute as expected.

But the main benefit of API test automation—and test automation in general—is that it avoids regressions. With a comprehensive test suite, developers have a safety net that tells them when they break something after a change. With test automation, teams have the confidence to ship new code at the speed users and the market now demand.

Overview of API test automation

How does API test automation work? First of all, you need to understand that there a variety of types of API testing. When it comes to functionality, you can leverage functional or end-to-end testing to validate that the inputs and outputs of endpoints are handled corrected, to test whether error conditions return the expected responses, and that the externally observable results happen as expected—for instance, validating that a message is published to a message bus as expected, after a POST request to a given endpoint.

When it comes to the performance of your API, several types of testing can be leveraged, such as load testing (how the API performs under normal circumstances), stress testing (how the API responds under peak loads), and endurance testing (how the API handles continuous load over time).

Finally, don’t forget that APIs are interfaces. As such, they are also contracts, they define the rights and obligations of two parties that need to collaborate. So it’s vital to use some form of contract testing to test both the contract of the third-party APIs you mock when developing your software, and the contracts of your own APIs, so changes to them don’t break backwards compatibility and upsets your users.

Best Practices in API Test Automation

Here’s a non exhaustive list of best practices you should be aware of.

Use version control and CI/CD

This is somewhat basic but it’s worth mentioning. If you have tests that are code-based, add them to your version control system. Also, and this should be mandatory, make sure your tests run in your CI/CD pipeline.

Don’t test only the happy path

A frequent test automation error is only testing the happy path. Things go wrong often and your tests must also ensure that, whenever things go south, the error handling portion of the application works as it should.

Implement automatic refreshing of expired tokens, implement token management, andstore credentials securely

Handle authentication efficiently

Ensure you handle authentication in an efficient, safe manner. Implement automatic refreshing of expired tokens, implement token management, and store credentials securely.

Start testing as early as possible

Finally, shift-left as much as you can by starting testing at the earliest possible moment. You might wonder how you can start testing if you depend on a third-party API that’s still in development. The answer is to leverage tools that allow you to simulate, or mock, those systems. When the time comes, you can safely replace the simulations with the real thing, in the production code.

Conclusion

APIs (particularly web APIs) play a big role in modern software development. That’s why API test automation is so crucial: it helps teams ship features to their APIs at the speed the modern world demands, while keeping quality high at the same time.

In this post, we’ve offered you an introduction to API test automation. You now understand what APIs are and why automating their testing is so crucial. Thank you for reading.

This post was written by Carlos Schults. Carlos is a skilled software engineer and an accomplished technical writer for various clients. His passion is to get to the bottom (the original source) of things and captivate readers with approachable and informative technical content.