Testing an API is a broad topic and can be a complex process, though, with the right tips and tools, the process can become much simpler. However, there are many types of API testing, so it is good to start off by getting a clear definition of the types of API testing. In this article, we explore the different types of API testing, some API testing tools, and top it all off by providing developers with tips to improve the API testing process.
API refers to Application Programming Interfaces. It is an internal interface working as a connection layer between two other parts of a software system: the presentation (UI) layer and the data layer. The easiest metaphor to explain API is the waiter who facilitates communication and data exchange for the user. API also includes the business logic or how users will actually interact with the functions and data of the application.
API testing aims to make sure the application efficiency is optimized. Most applications consist of several layers: user interface, database, and the business layer. API testing is needed primarily for the business layer since it handles most of the logic and business operations, user interface, and database transactions.
The main goals of API testing are checking development and coding content in order to enhance its performance and function. In order to perform API testing better, you should first understand the different types of API testing, which we cover below.
What is API Testing?
In light of API sensitive jobs and applications that rely on APIs, it is critical to test APIs, especially those that focus heavily on the UI. Testing APIs mainly aims to:
- Validating the response for requesting single or multiple API endpoints calls.
- Checking API general performance, jams, and efficiency.
- Testing the API general security and authentication for possible gaps.
- Checking API general status for quality control purposes.
- Testing the API business logic in general and for data responses.
API Testing is performed through special software tools that send specific calls to the API and examine the outputs against expectations. It is different than Graphical User Interface (GUI) tests because it places the focus on business logic instead of the user experience.
API Testing has many benefits, including:
- Earlier Testing: Allows developers to check data responses earlier; testing can be performed once the logic layer is ready and before the final stage of work.
- Easier Test Maintenance: It’s much more stable than UI tests, which change every day. It can also be implemented quickly.
- Faster Time for Fixing Bugs: If the API test result is bad, it helps to diagnose where the problem is in the system, leading to faster bug detection.
Types of API Testing
API Testing types can be classified in different ways. Below are some of the common types of API testing:
- Functional Testing: testing functions based on the code.
- User Interface Testing: testing how easy it is to use and access the application.
- Security Testing: to make sure of the application’s safety against threats.
- Load Testing: testing the ability to withstand heavy load.
- Runtime & Error Detection: to make sure it’s empty from errors.
- Validation Testing: verifying the final efficiency, behavior, and other functions.
- Fuzz Testing: to rule out any possible negative behaviors.
It can also include:
- Unit Testing: testing manually one endpoint by one call waiting for one response.
- Integration Testing: It’s the most common API testing type.
- End to End Testing: in order to verify the data influx through some API connections.
- Performance Testing: It became embedded in CI/CD recently thanks to ReadyAPI.
API Testing Tips
Below are some tips for API testing best practices to help you achieve more professional tests and results:
- Knowing API requirements: such as understanding API’s purpose and workflow. This will help to prepare a better validation approach versus specific data or other APIs.
- Determine the API output status: Knowing the required status code responses to consider they passed or failed according to the global five classes standard.
- Begin with small functional APIs: starting with some small inputs like login API can open the door of API functions since it ensures API environment first.
- Keep testing a single API each time: to avoid a backlog of error messages, except for cases that need a series of API testing.
- Organize API endpoints: between a few to tens of APIs for tests; it’s better to classify them into categories for easier management.
- Take advantage of automation: it’s advised to leverage any automation abilities in an early time to save the execution history for return later as a black box.
- Choose a suitable API automation tool: it’s better to take the best ones that support your API types, authorization, endpoints, and other needs.
- Choosing suitable verification methods: to help validate the type API response body content either as plain text or XML document.
- Implementing positive and negative tests: to make sure the API is working properly. This will help validate receiving input returning the desired outputs.
- Live testing process: putting daily API test executions is advised for it’s easy and doesn’t cost a lot. This will also help test API’s behaviors in various authorization levels.
- Take automation seriously: despite the first tests being simple, the next testing tasks become more difficult each time for the APIs. Automation makes it reusable.
API Testing Tools
In the past, there were very few API testing tools, but recently more have arrived on the scene. Every API tool has its own unique set of features. Here are some popular API testing tools:
- SoapUI– SoapUI: It’s the most common globally. It’s used to test REST and SOAP APIs quickly and easily. Many major brands use it such as Apple, Microsoft, Oracle.
- Katalon Studio: It enables users to perform API tests even without previous experience. It supports REST of all kinds and provides detailed report results.
- Apigee: It’s one of the cross-cloud tools to empower deploying APIs and create proxies for them. In addition to diagnosing performance faults.
- Tricentis Tosca: It’s a great tool for web services APIs, it supports many web protocols and it merged with DevOps agile cycle. And used in the mobile.
- Postman: It’s used as a Google Chrome plugin for testing all modern web services APIs. It also helps to write Boolean tests and collect REST calls for later.