API Testing: Delivering Healthy and Performant APIs

API testing is a type of software testing that falls in the category of integration testing. It is a white box testing technique. API testing is performed in order to ensure that different software components interact correctly with each other and their designated interfaces. API Testing is performed by executing the individual software modules through an interface. The aim of API Testing is to verify both functional and non–functional requirements (e.g., response time).

API testing determines the functionality, efficiency, reliability, and security of Application Program Interfaces (APIs). It guarantees that your APIs are healthy and that you can use them reliably and safely in your applications.

APIs provide the interaction, sharing, and communicating of information easily between software systems. APIs play a critical role in the software development process. APIs are extremely important in the software development process. As a result, executing API tests might identify abnormalities that may hamper their correct functioning and put the development process or program in jeopardy.

This blog article will go through how to test your APIs so that you can get the value you expected from them.

What Is API Testing?

API testing is a type of software testing that verifies and validates if APIs meet the expected performance requirements.

It involves performing a set of quality assurance actions to discover faults in the API design, identify any errors or gaps against the expected outputs, and find how to improve the APIs’ functionality.

End-to-end API testing is usually done on APIs that the in-house development team creates. For third-party APIs (those that are consumed), the tests aim to check how the applications that depend on them accept their requests.

Testing APIs commonly involve testing SOAP APIs, GraphQL, or REST APIs—with XML or JSON message payloads transmitted over HTTP or HTTPS. Because of the popularity of the REST architectural style, REST API testing is widely practiced among API developers and consumers.

Where Is API Testing Done?

Most modern applications are usually designed using the “layered architecture technique.” This involves creating applications that have the following three separate layers or tiers:

• Presentation layer—this is the user interface (UI) layer.
• Business layer—this is the application user interface for processing business logic.
• Database layer—this is the layer for manipulating and modeling data.

API testing is done at the business layer, which contains the application’s core functionality.

This layer has a series of discrete but interconnected components responsible for carrying out business logic processing and handling communication between the UI and the database.

Since an API sits at the critical layer in the software architecture, ensuring that it works as intended is essential for the application’s optimal functionality.

Furthermore, API tests are different from GUI (graphical user interface) tests—they do not focus on the application’s look and feel. Running tests on APIs mainly focuses on the application’s business logic without involving the GUI.

How Is API Testing Done?

Typically, API testing is done by making calls to the API, getting the output, and analyzing the results.

Let’s talk about the steps you can follow to perform tests on your APIs.

Step 1: Understand the API’s scope

You need to start by having a full understanding of how the API is supposed to work. This will help you plan appropriate tests throughout the testing process.

These are some questions you can consider:

• What is the API’s purpose and its target consumer?
• Are there other APIs this API interacts with?
• Which endpoints can be tested?
• Which response codes are generated for successful requests?
• Which response codes are generated for failed requests?
• Which error messages appear in the body of failed requests?

Step 2: Set up a test environment

After determining the API’s functional scope, the next step is establishing an API test environment. The environment will help you make API requests and assess the responses.

There is a wide range of API testing tools you can use to set up an environment for testing your APIs. For example, the Rakuten RapidAPI is an expansive API marketplace that allows you to find, test, and connect to thousands of APIs. It comes with a comprehensive environment for deep validation of APIs.

Step 3: Create and run test cases

After completing the preparation process, you can create and run API test cases. These tests will stipulate the variables or conditions you’ll use to determine if the API performs as desired.

After running the test cases, you can compare the actual results with the expected results. You need to provide all the possible input combinations that will enable you to execute satisfactory test cases.

Here are some examples of test cases:

• Testing the response value based on an input condition. This involves defining the input and authenticating the output to determine if the API works as intended.
• Evaluating the API’s behavior in case the response does not have any return value.
• Testing the events or actions triggered by an API’s response.
• If an API call modifies certain resources, tests can be run to validate them.
• Testing the API’s maximum response time.
• Testing if the API can handle the expected user load.

Running test cases can reveal various defects in your APIs. Here are some of them:

• Unused flags
• API security issues
• Improper handling of errors
• Improper handling of valid or invalid argument values
• Dysfunctional features
• Performance and reliability issues, such as delayed response time
• Incorrect formatting of the response data
• Inaccurate response data

Types of API Testing

Several tests can be performed on APIs.

Typically, they can be categorized as follows:

• Validation testing
• Functional testing
• Performance testing
• Security and compliance testing
• Integration and reliability testing

Let’s address each of them in detail.

1. Validation testing

Validation testing plays a critical role in the API’s development process. It assists in verifying the API’s capabilities, efficiency, and behavior.

Validation tests ensure the API is developed well and able to meet the required users’ needs.

2. Functional testing

Functional testing assesses specific functions within the API’s codebase. It ensures the API is operational and can do what it’s supposed to do.

Functional tests guarantee that the API works within the expected parameters—for a given input, it returns the expected output; and if the results are beyond the designated parameters, it handles the errors gracefully.

Here is an example of a functional test done on the Deezer API on the Rakuten RapidAPI platform:

Other types of functional testing are positive testing and negative testing. In negative testing, the tester provides wrong inputs to the API and assesses how it responds to them.

In positive testing, the tester provides the right inputs and verifies whether the API functions as desired. In case the positive API tests fail, it implies that the API cannot work well even under ideal situations.

3. Performance testing

Performance testing ascertains if the API works at optimal capacity. It verifies various API’s diverse operations, such as functionality, speed, reliability, and response time.

These tests do not concentrate on the API’s defects, but rather on finding out things that may impair its proper performance.

Here are some common types of performance testing:

• Load testing—it checks the API’s capability to handle the expected or higher loads. The server conditions, throughput, or response times can be measured while gradually increasing the number of API calls.
• Stress testing—it involves progressively increasing the number of API calls to identify the point when the API begins throwing errors, slowing down, or stopping to respond.
• Spike testing—it involves subjecting the API to a sudden spike in usage. It checks if it can stabilize and revert to normal performance after that spike.

The stress described above, exercises API functions to determine how well it holds up when faced with a surge in demand. For example, if you have a Finance API with millions of API calls per day on average. But when markets are volatile, calls to your API can increase by order of magnitude. Does your API still work? What about if there is no warning — just hundreds of thousands of API calls come in one minute? Does your server continue to respond quickly and accurately? That’s what stress testing does — it finds out if the hardware can handle sudden changes in demand without slowing down or crashing altogether.

These tests tests also look at network bandwidth capabilities by pinging test servers from multiple locations simultaneously to simulate user loads on a production environment. This helps identify issues such as network congestion that can slow down operations until data centers can manage them properly.

Such tests also checks response time by running automated scripts simultaneously from multiple locations worldwide, so they appear like thousands of real users accessing your API at once.

4. Security and compliance testing

Security and compliance testing validate if the API meets the stated security requirements.

Here are the main types:

• Penetration testing—it involves simulating an attack against the API to discover exploitable vulnerabilities. If any security loophole is identified, it’s corrected before an attacker takes advantage of it.
• Fuzz testing—this is a security audit technique that tests the API’s limits to imitate worst-case scenarios. It involves bombarding the API with a large quantity of random data, called “fuzz” or “noise,” to uncover any abnormal behaviors or crashes.
• Compliance testing—this checks if the API conforms to various data compliance regulations and industry standards, such as GDPR, HIPAA, or PCI DSS.

What is API Fuzzing?

Web API fuzzing is a process of testing your API backend for bugs and potential security issues. It does this by setting the parameters to unexpected values. API fuzzing may cause errors and unexpected behavior in the API backend and discover possible vulnerabilities that other QA processes might have missed.

5. Integration and reliability testing

Since APIs support integrations between disparate systems, they need to be subjected to the following tests:

• Integration testing—it focuses on exposing faults in the interaction between APIs. This test ensures the APIs are well connected and can communicate with each other flawlessly.
• Reliability testing—it focuses on ensuring the API is reliable enough to be connected to and produce consistent results. If synced with different devices, disconnections can make the API unreliable.

Benefits of API Testing

Here are two of the main advantages of testing APIs:

a. Language independent

You can test APIs in any of the popular programming languages. APIs exchange data using various formats, such as JSON and XML, which are not dependent on any language.

JSON and XML are essentially structured data formats. This allows for stable and fast testing.

b. Productive and efficient testing

You can perform API tests in the application without depending on the GUI. This lets you identify bugs that may not be discovered from GUI testing.

Running user interface tests usually do not focus on all the essential aspects of back-end testing. This could allow bugs to remain in the server or unit levels, leading to costly development mistakes.

With API testing, you can begin testing the application early, even before the user interface is ready. This lets you discover and correct bugs early, expose hidden errors that may impair the application’s functionality, and release software faster.

Challenges of API Testing

Whereas testing APIs has various benefits, it also presents some challenges. A major challenge API testers often face is the sequencing of API calls.

If the requests must be in a specific order for the API to work correctly, it may be challenging to get it right.

For example, if a request to return a user’s account details is sent before sign up, the call will produce an error. This can become even more complicated when multithreaded applications are involved.

Another challenge of testing APIs is selecting proper parameter combinations. When an API’s feature depends on combining different parameters, testing all the possible combinations to detect problems may be demanding.

Testers may find it difficult validating the different parameters, ensuring every parameter data uses the right data type, or passing other validation criteria.

Best Practices for API Testing

Let’s talk about some API testing best practices you can use to get the most out of your testing efforts.

a. Select a suitable tool

Going for the right tool could help realize your goals of API testing. With a suitable API testing tool, you can automatically carry out various test activities, write tests for maximum coverage, and stay ahead of the game.

Later in this article, we’ll talk about how to use the Enterprise Hub testing tool to take your testing efforts to the next level.

b. Group tests by category

If you want to test a wide range of scenarios, you can group the related test cases into categories. This will enhance test management, make your tests reusable, and save on time and resources.

Furthermore, since APIs in the same category share some common functionalities, it would be easier to prioritize the tests to perform and create tests to handle unexpected issues.

c. Decide between manual and automated testing

You should know when manual testing or automated testing is suitable for your specific use case. While both types of tests have their own advantages and disadvantages, knowing when to choose one over the other could help you identify and fix bugs in APIs effectively.

For example, you should go for manual testing when performing usability testing and ad-hoc testing. On the other hand, you should go for automated testing when performing functional testing, repeated testing, and performance testing.

d. Practice effective test reporting

Practicing good test reporting will help identify weaknesses and strengths during the testing process and add value to test management. If the report is poorly written, it could lead to serious misunderstandings between the API developers and testers.

The bug report should clearly explain the problem in the API, include step-by-step instructions on how to reproduce the anomaly, and provide actionable insights on the issues encountered.

Using the Enterprise Hub for API Testing

The Rakuten RapidAPI Enterprise Hub is a comprehensive and easy-to-use API platform that comes with a wide range of capabilities for testing your APIs—from development to deployment. It’s enterprise-ready and supports on-premise testing.

The Enterprise Hub is one of its kind API testing tool. It ensures your APIs work as desired, meet your business requirements, and deliver the value you promised to your users.

Here are some amazing features that make the Enterprise Hub ideal for API testing:

• It provides an intuitive interface that lets you create complete and customizable functional API tests. You can use it to generate visual tests, automated tests, or code-based tests.
• It supports any API type. You can use it to run tests on your REST APIs, GraphQL APIs, or SOAP APIs.
• It allows you to secure every step of the API testing process via injection flaw testing, OAuth2/OpenID Connect, header validation, and more.
• It lets you centrally monitor your API tests to ensure their optimal performance. You can use it to create multiple tests across different environments simultaneously, get detailed execution reports, and receive real-time alerts whenever tests fail.
• It comes with built-in collaboration capabilities for organizing testers into teams and assigning API test permissions.
• It allows you to automatically import APIs published on the Rakuten RapidAPI marketplace platform to speed up their testing process.
• And many more…

You may contact us right now to start using the Enterprise Hub for testing your APIs. It’s the solution you need to ensure your APIs are healthy and performant.