API Testing: A Cheatsheet for Development Teams

What Is an API?

Just in case this topic is new for you, an API is an abbreviation for an application programming interface. It is a contract introduced by a software program that allows using any features of a particular system in a different place.

Technically, one software system agrees to address the other in a specific way. In turn, this other system guarantees to respond with the necessary information or process this data in a specified way.

Some say the best analogy to an API is an agreement. The others explain its role as an intermediary that enables clear communication between the parties. If we are to draw a parallel between an API and something familiar from our daily routines, the closest example would be ordering a meal at a restaurant.

A visitor sees a menu, chooses something, and informs a waiter. The waiter communicates it to the kitchen and comes back with the food. A guest doesn’t go to see the kitchen staff in person. Instead, there is a third party that enables their interaction and communication. That’s what an API does for software systems.

Why Do We Need API Testing?

All types of testing are meant to prevent critical bugs in production. So let us paraphrase the question: what types of mistakes does API testing help detect? This list includes:

• Data transferred incorrectly and error condition failures.
• Missing or duplicate functionality that affects system efficiency.
• Security breaches and potential threats of various complexity and severity.
• Issues with connecting to other systems through an API or receiving a response.
• Slow request processing that makes it difficult or impossible to complete an action.
• Multithreading issues that slow down the system.

API Testing: Rewards for Software Production

Benefits of API Testing

As you can see from the list above, API testing allows us to detect serious issues that interfere with business performance. However, API testing also has specific advantages for different members of a project team.

For developers, it becomes much easier to find the root cause of the problem.

When a software tester sends a request to an end-point during API testing, they receive an error with a code and descriptions and see a stack trace. This information is key to solving the problem. By sharing the findings, a QA specialist points out a problematic part of the code to a developer.

Meanwhile, when testing the same functionality through a user interface, it is not always possible to understand what exactly causes the problem. Maybe a client doesn’t gather the data correctly. Maybe a server doesn’t read it properly. As a result, the team cannot be sure whether the problem lies in the API while the interface works perfectly or vice versa.

For software testers, it takes less time to prepare test data.

Let’s say a QA engineer needs to prepare specific datasets before test execution – fill in the 40-row table with specific data or something like that. Usually, in API testing, they need to do it just once. Then, a QA specialist can look at where a browser sends the test data and automate the tests. Thanks to API automation testing, it becomes much easier to work with large data sets.

For stakeholders, it becomes possible to speed up the release thanks to the early testing.

A development team creates and finalizes a user interface at the later stages after the infrastructure and back-end are ready. Meanwhile, we all know about the benefits of early testing. It helps speed up the development, refine the code, and reduce the price of mistakes. Luckily, API testing doesn’t rely on the graphical user interface. Thus, a QA specialist can work with APIs even before the front-end is ready.

Marketplace case in Tokyo: API Service Testing, Transition from Python 2 to Python 3

Types of API Testing

There are several types of testing to run for an API. Each of them focuses on a different aspect and is equally important. Below are brief explanations you may find useful when considering the development timeline or planning the QA activities.

• Functional testing, as you may already know, is meant to verify the features of the tested software against the requirements. In this case, we are speaking specifically about API functionality. Therefore, this group of tests should cover a set of API calls to check the overall system health. In the end, why do we need an API that doesn’t perform an intended function?
• Security testing focuses on authentication details and data encryption. Sometimes it turns out that an API is not protected at all. As a result, an end-user can easily modify system data using an unprotected API’s endpoint, causing serious problems. This is where a security audit comes in handy, helping to detect and fix the vulnerabilities.
• Documentation testing means checking the consistency, completeness, and clarity of the documentation that describes API functions. You can often find documentation testing on the list of QA services offered by software testing companies. A thorough check of the specifications can help detect issues even before the implementation, once again making the development process more efficient.
• Usability testing is all about the convenience of the API interface. We don’t run the full-scale UX testing, but even a quick basic overview of UI elements that enable an API allows us to learn whether it will be convenient to operate for end-users.

API Automation & API Testing Tools

API testing is a perfect candidate for automation. By preparing the scripts and setting up applications to run the repeated tests, QA engineers can spare time for other tasks and increase the accuracy of the testing results. It is especially important if you have to deal with large datasets, which is a usual situation for APIs.

The selection of tools for API automation depends on the tech stack of the discussed project. While the most common cases are working with REST API and Postman API testing, our QA engineers always discuss the preferred solutions with the client’s tech team.

Automated Testing Goals & Objectives

To Sum Up

You can’t say API testing is more essential than other QA activities, but it is certainly one of those you shouldn’t consider skipping. Even if you have the most talented and attentive dev team, creating a bug-free product from the first take sounds more like a fantasy than a real scenario. Defects are unpredictable. They are an unknown variable in every development process. And they tend to pop up at the seams, where smaller components and subsystems are integrated – by APIs as one of the means to connect the functionalities.