In other videos and articles, we studied what APIs are, and APIs types, and got familiar with REST APIs in detail. In this article, we will talk about API testing and why it is important.
API testing is a type of software testing that involves testing application programming interfaces (APIs) directly. The goal of API testing is to determine if APIs meet various types of requirements: functional, reliability, performance, security, etc.
The API testing process involves sending various requests to the API, including requests for valid and invalid inputs, as well as requests for specific scenarios, such as error conditions or load testing. The response is then checked to ensure that it meets the expected results based on the requirements.
Some common types of requests that are sent during API testing include GET, POST, PUT, and DELETE requests. These requests are used to retrieve data, create new resources, update existing resources, and delete resources.
This can be done manually or using automated testing tools. Testing tools for API automation can be used to streamline the testing process, reduce manual effort, and increase efficiency. These tools can automate the process of sending requests and verifying the responses, as well as perform load testing and security testing.
There are many reasons why API testing is important and there are many benefits that it brings, but we will highlight only the three biggest advantages:
First, Early feedback. Applications often have three layers: a data layer, a service (API) layer, and a presentation (UI) layer. The API layer contains the business logic of an application — the rules of how users can interact with services, data, or functions of the app. Many teams adopt the API-first development model, in which applications are conceptualized and built as a collection of internal and external services that are delivered through APIs. It means that typically developers create the APi first, and then the UI can be built on top of it. If the test team doesn't conduct API testing, but only UI testing, then during UI testing testers will find two types of bugs. UI bugs, which are often called front-end bugs. And API bugs, often called server-side bugs or backend bugs. The back-end bugs often are blockers, you can't test UI if the server doesn't send any responses or the wrong responses. Due to blockers, the test team will not be able to continue testing, because they are blockers, and will wait until the developers fix the bugs on the server side only then will the test team be able to test the integration of UI with the API, and UI itself. If API testing is conducted, then it is mostly conducted in parallel with the development of UI. While front-end developers create UI, testers conduct API testing, and back-end developers fix API bugs and server-side bugs. Thus, in the vast majority of cases, by the time the frontend developers finish their part of the work, API testing will be completed, and backend bugs will be fixed. And when the test team starts testing UI, it will face a much smaller number of blockers.
Second, efficient bug localization. This advantage of API testing is closely related to the first advantage. Let's imagine that a new build is ready for testing, and the test team only has UI test cases. Even if they are automated, they have one disadvantage - without debugging, it is unknown where the error occurred. If the test failed due to an error, say some data was not displayed in the form, all the tester will see is that there is no data in the form on the screenshot, and it is unclear why there is no data. It may be that the test itself is broken and needs to be updated, it may be that the UI has been changed and because of this the test failed, or it may be that the server did not return the data, in order to find out what exactly went wrong, you need to debug. If, in addition to UI tests, the test team has API tests, then when running the test case it will be immediately clear that the server is behaving incorrectly, accordingly, there is most likely no point in running UI tests because there is a great risk that many tests will fail due to incorrect behavior of the server.
And this brings us to the last important advantage of API testing, API tests are easy to automate and faster to execute. There are many tools available for API testing automation, like Postman, SoapUI, JMeter, etc. With minimal knowledge of a programming language, mainly JavaScript, API tests are very easy to automate and execute using these tools. Automated API tests can be run on demand or as part of a continuous integration and delivery (CI/CD) pipeline, providing faster feedback to developers about potential issues or regressions in the code. Since API tests typically involve less overhead than UI tests, API tests can be run more frequently, providing developers with more timely and accurate feedback. However, it's important to note that automated API tests alone may not be sufficient to fully validate the application's functionality. UI tests are still necessary to validate the application's behavior from the user's perspective, and to ensure that the UI elements and user flows are working as intended. Therefore, a balanced testing strategy that includes both API and UI tests is typically recommended.
API testing is a type of software testing that involves testing application programming interfaces (APIs) directly. The goal of API testing is to determine if APIs meet various types of requirements: functional, reliability, performance, security, etc. There are many reasons why API testing is important and there are many benefits that it brings, such as early feedback, efficient bug localization, easy automation, and faster execution.