An Overview of API Testing: Types, Benefits and Drawbacks | TestDevLab Blog

An Overview of API Testing: Types, Benefits and Drawbacks

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It's no secret that software testing plays an essential role in developing a successful app. And at one point or another you will eventually encounter the concept of API testing, which is actively used by QA teams and software developers. In fact, statistics reveal that almost 90% of developers use APIs in some capacity. So they’re a pretty big deal. Think of an API as the middleman that allows programs to communicate with each other, giving software developers a chance to develop their products easier. In this blog post, we will discuss API testing in general, explore the different types of API testing, and look at their benefits and drawbacks.

What is an API?

API stands for Application Programming Interface and is a software intermediary that defines a standard for communicating between two programs. It allows end users to communicate with backend services through a user interface, also known as a frontend, by hiding all business logic and presenting only the necessary pieces of information to end users.

Although API roots can be found as far back as the 1940s, modern APIs as we know them today started to appear not so long ago in the early 2000s. Today when we hear about an API, it almost always references our modern API approach which uses HTTP (Hypertext Transfer Protocol) that provides data in machine-readable formats JSON or XML.

Examples of APIs

The best way to explain what an API is—and the easiest way to understand it—is by comparing an API to a waiter. Imagine you’re at a restaurant. You’re holding a menu and thinking about what to order. When you’re ready to order, the waiter comes and takes your order to the kitchen—the same way an API delivers a request. Then the kitchen—acting like a data server—prepares the order and when it is ready, gives it to the waiter (API) to take to your table. In this example the waiter is the API that is facilitating communication between two separate systems, in this case you and the kitchen.

API request and response

Another example of an API at work can be seen in weather apps. Have you ever wondered how your phone weather app always has information about upcoming weather forecasts? Well, the weather app on your phone communicates with the data server via APIs by sending and receiving data, and then presents this data in your phone app in a readable way.

Ecommerce websites would be another example of where APIs are used. Let’s say you are trying to shop for a brand new TV. First, you want to filter particular sizes, brands, and colors. You set preferred filter settings and click on search. At this moment you're interacting with the store’s website to access their database by sending a request to the database with the desired values you selected. After the database gets a request, it proceeds with a response by sending data about all available TVs with specific values. When a website receives a response from the database it presents this data according to your specifications.

What is API testing?

API testing is a type of software testing practice that examines APIs in depth as well as in the context of integration testing to determine whether they meet expectations in terms of functionality, dependability, stability, and security by evaluating server answers. Unlike UI testing, API testing does not focus on the look and feel of the app. Instead, it mainly focuses on the business layer by generally performing requests to API endpoints and comparing results with expected ones. API testing is more dependable and may be finished more quickly, which is why automated API testing has become crucial and broadly used in Agile software development.

Types of API testing

Various types of tests can be performed to ensure the API is operating appropriately. These tests assist in identifying errors and issues, excluding any duplicate or missing functionality, issues with dependability, security, and performance, as well as issues with the improper handling of arguments or parameters. If a product can’t be relied upon, it has no value. Therefore, it is important to ensure that the API is using resources correctly and in the intended way.

Although not all of these tests will be suitable for your codebase, implementation, and specific use case, it is more likely that some of them will be regarded as standard for the typical web API development lifecycle.

Validation testing

Validation testing is performed at the final stage of the development process, but at the same time, it’s one of the most important API tests. The goal of validation testing is to verify aspects of the product, its behavior, and efficiency. To do this type of testing, there are a few simple questions that need to be answered about:

  • Product. Is the correct product built?

Is the API the right solution for the problem that was described, and did it suffer from any substantial code bloat or feature creep that turned an otherwise lean and focused implementation into something that couldn't be maintained?

  • Behavior. Is the API using the proper defined methods to access the right data?

Given the confidentiality and integrity requirements of the dataset, is the API accessing too much data and does the API expect necessary data to be provided?

  • Efficiency. Is this API the most accurate and effective way to complete a task?

Can any codebase be modified or removed entirely to lessen flaws and enhance overall service?

The purpose of these questions is to effectively verify the API as a comprehensive solution. They are made after the API is developed in accordance with predetermined criteria to guarantee proper environment integration, adherence to rules, and the accomplishment of particular end objectives and results. In short, it can be said that validation testing provides assurance of proper development in relation to the given user demands and criteria.

Functional testing

Functional testing is basically testing particular codebase functionalities. It evaluates the responses based on the accuracy of the output and whether it is within a predetermined threshold, and how errors are dealt with when the results fall outside the specified boundaries.

UI testing

UI testing in many ways is a more specific type of testing because it analyzes the interface that is connected with the API and the developer's experience using this interface instead of the API itself.

UI testing provides a fairly broad overview of the health, usability, and efficiency of both the frontend and backend, despite the fact that it is not a specialized test of APIs in terms of the codebase.

You might be interested in: Automated UI Testing for Mobile Apps Using Bluetooth Mouse

Load testing

Load testing is used to see how many calls an API can handle at a certain time to find performance bottlenecks before production deployment. This is often done by reusing functional test cases to validate performance and functionality under load. A specific unit or the entire codebase is tested under a certain load by gradually increasing the number of requests from 1,000 to 10,000 to 100,000, and so on, to determine how effective the theoretical solution is.

There are three levels of API load testing: baseline or regular, maximum load, and overload which is a theoretical maximum load plus an extra 15-20%.

Security testing

A lock on a laptop

The purpose of security testing is to make sure that API implementation is secure from external threats which include validation of authentication checks, encryption methods, and access control design. An API provides access to all external applications, that’s why it is usually considered the most exposed or vulnerable part of the system. A single vulnerability or bug can have serious consequences.

Penetration testing

Penetration testing is a security testing subgroup. The purpose is to find vulnerabilities that could be exploited by an attacker. In penetration testing users with limited knowledge of APIs evaluate the threat vector from an outside perspective, which could be based on certain functions, resources, processes, or the API as a whole.

Fuzz testing

Fuzz testing is another subgroup of security testing, however, it is not as sophisticated as penetration testing or the testing types listed earlier. The goal of fuzz testing is to attempt to force a crash, overflow, or negative behavior of an app by forcibly inputting a massive amount of random data (referred to as "fuzz" or “noise") into the system. This serves as a sort of "worst case scenario" and allows the API to be tested to its absolute limits.

Runtime error detection

In contrast to other types of API testing practices, runtime error detection is only interested in how the API really functions. It evaluates the outcomes of applying the API codebase, focuses on execution errors, tests the system's error-handling abilities, and keeps track of memory leaks. Runtime error detection is intended to comprehensively verify that fixes have been made after a near-final assessment of the known defects and issues produced by earlier tests.

Benefits of API testing

In short, API testing can improve test coverage, save time and resources to release apps, and protect apps from malicious code or cyber attacks. Here are some of the benefits API testing offers:

Saves time

API testing can start very early in the development cycle at integration level testing and doesn't need the GUI to be ready. API tests deliver test results much faster and significantly speeds up development processes. As a result, you can shorten the feedback loop and identify errors more quickly.

While API tests can be executed in a few seconds, UI tests take more time to display and load the web pages and interface elements.

Lowers expenses

Reduced costs and time efficiency go hand in hand. API testing gives the advantage of identifying issues early in the SDLC by starting testing as soon as business logic is defined and before UI testing. It enables issues to be fixed before they affect production. Early detection lowers the cost of application changes and lowers the cost of fixing the issue. Also, automating API tests requires less code than automating GUI tests, which ultimately speeds up testing and lowers testing costs.

Language independent

Since the data is exchanged using JSON or XML formats and compromised HTTP requests and responses, API tests can be performed in any language and are completely independent of the application language. This means that any programming language that supports these technologies may be used without restriction by the QA engineers (JavaScript, Java, Ruby, Python, PHP, etc.).

Greater test stability

API interfaces, especially when exposed to third parties, are much more stable than UIs, which tend to change, due to their dynamic nature to accommodate new requests from stakeholders and users.

Any changes to the APIs are typically reflected in the extensive documentation that typically accompanies them, allowing QA engineers to promptly modify their test suites. This makes API tests less maintenance-intensive and results in fewer false negatives from out-of-date tests.

Improved test coverage

The majority of API services have specifications, allowing you to build high coverage tests that cover both functional testing and non-functional testing to ensure that all system components work as intended. It helps find potential flaws in the servers, databases, and interfaces, raising the overall software quality and enhancing user experiences.

Multiple platforms covered

When the same app is made available for several other platforms like mobile, desktop, etc., the same set of APIs is used. Therefore, when we test an API collection, we also make sure that the business logic will execute consistently across the various platforms leading to saved time and costs.

Drawbacks of API testing

QA engineer pointing something out on a laptop to a colleague.

Despite the fact that API testing has many benefits, it also has some drawbacks, which we will look at in more detail.

Technical skills

Those who have never tested APIs before may find it difficult to get started. The creation and launch of the API test environment, as well as the development and maintenance of automated tests, may become challenging. It requires the QA team to have certain technical skills and often programming language experience.

The absence of a user interface to test an API can also be confusing for software testers with no previous experience in API testing. Therefore, before beginning the task, less experienced software testers might need some time to become more familiar with the API and its testing.

UI validation

In case the tests are performed only at the API layer, you can be sure that the data is handled correctly, but that does not guarantee that the user can interact with the application in an expected way. API testing does not cover user interface risks. Therefore, UI and API testing should be combined.

Parameter selection, combination and call sequencing

The parameters sent through API requests must be validated before being used. Testers must ensure that all parameter data satisfies the validation requirements, including the use of appropriate string or numerical data, a given value range, and adherence to length restrictions.

Combining parameters can be difficult because each combination must be tested to see if it contains issues with particular configurations. Because every call must appear in a specific order to guarantee the system functions properly, call sequencing can become a challenge. This can quickly turn into a problem, particularly when working with multithreaded applications.

Key takeaways

API tests are a great approach to test data handling and processing of applications. They offer access to various systems without a UI and offer a higher ROI than UI testing by allowing developers to detect and fix defects at an early stage in the SDLC.

Insufficiently tested APIs may result in problems for both the calling application and the API application. API automation testing is a great practice that significantly improves the quality of the application in short cycles. It is a crucial software engineering test, but at the same time, it's important to keep in mind that the frontend cannot be disregarded, and sanity tests should be implemented to address these risks.

At TestDevLab, we offer a wide range of API testing services that detect API connection difficulties, false errors, security issues, incorrect data structuring, and other inconsistencies. Contact us to learn more about our API testing services and how they can benefit your organization.

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