Test automation experts use API testing to receive quick feedback and improve product quality. This article will share why API testing is a necessary component of your automation suite and what the benefits of implementing API testing are. However, before diving in, we first need to understand what the API is. The API, or Application Programming Interface, allows communication and the free exchange of data between two software systems. A good API makes it easier to develop a program by inherently providing many of the necessary building blocks. Let’s get started!
What is API Testing?
Application Programming Interface testing, also known as grey box testing, are functional tests on the back-end that focus on determining if the API implementation meets expectations regarding functionality, performance, reliability and security. API testing is essential for product quality and CI/CD processes. It also mainly concentrates on the business logic layer of the software architecture, as shown in the image below.
Benefits of API testing
QA teams should prioritize API testing as it provides a number of benefits including:
- Easier performance testing – it helps to determine an application’s limitations under expected concurrent load. This, in turn, helps with addressing performance issues and provisioning the right resources as user traffic increases.
- Enables faster releases – we don’t need to wait for any team to finish their code to test it, because test cases are independent and ready to build instantly. As opposed to UI tests, API test execution saves a considerable amount of time.
- Fast feedback – feedback provided by UI tests is much slower than feedback from API tests, because it requires less code (no GUI needed) and reduces overall testing cost. Furthermore, API testing can be performed while the GUI is in development, and this helps with fixing issues as soon as possible.
- Pipeline integration – run your API tests at build time or on a regular schedule. The cadence depends on the scale of your application and how often your code base changes. There are a lot of tools that can help you to easily integrate and manage it, such as POSTman.
- Reliability of tests – if you make any change that breaks any test in the API suite, it will show you what’s failing, because they don’t need to wait for UI elements to render or async calls.
- Isolation of root cause – the defects can be spotted easily in isolation, because they are divided into modules.
- Improved test coverage – most API’s have specifications that help to create automated tests with high coverage.
- Reduce testing cost and easier test maintenance – during API testing we can find minor bugs before the UI is ready for testing. In other words, API testing will be cost effective. Another point is API changes are much more controlled and infrequent compared to GUI changes which occur more often.
How to Test Your API
We need to know what action or feature we will test and what is the endpoint to be tested. Then, we need which request method, that can be:
- GET: get data;
- POST: insert data;
- PUT: change or update data;
- DELETE: remove data;
The main validations that you should be aware of when you are testing an API:
- Validate returned status, header and body;
- Validate when your API is down;
- Validate returned response based on your requirements for each type of data sent through the API;
- Validate the API behaviour when you send a JSON/XML file with invalid structure.
Best Practices for API Testing
To help you along this path, follow these best practices to make API testing even more efficient:
- Include security tests in your suite to verify which type of authentication is needed, if data should be encrypted, and some other validations that ensure security;
- Invest in tools to automate your API and the data sent, so the process of executing calls will be much more efficient;
- In your test cases, insert the data structure that will be sent during execution;
- When you are writing your test cases, make sure which API will be called;
- If your API intersects with a system that you have access to, make a validation of results displayed on user interface (UI test).
Tools for API Testing
Before choosing the tool to perform your API tests, look for one that allows you to configure the header parameters, request method and body in a simple way. Some examples include SOAPUI, Postman, Curl, Cfix, Katalon Studio, and many more.
Conclusion
API testing helps us find inconsistencies or bugs from the expected behaviour of the API and should be prioritized by all QA teams. Ideally, we would follow Martin Fowler’s guidance on the Test Pyramid (here’s an interesting article written by our colleague Lucas Ávila) and also have unit and end-to-end tests. It’s one of the most important activities during the software development cycle, because if you find critical security and architectural defects early, they cost less money and are less risky to fix. API testing is very useful, fast and accessible if you have good documentation. They’re easier to maintain and provide quick checks of the build’s health. So, what’s holding you back from starting to test your APIs? Feel free to explore and take advantage of API tests.
This post was published under the Quality Assurance Community of Experts. Communities of Experts are specialized groups at Modus that consolidate knowledge, document standards, reduce delivery times for clients, and open up growth opportunities for team members. Learn more about the Modus Community of Experts program in the article Building a Community of Experts.
References
- https://www.guru99.com/api-testing.html
- https://medium.com/@aleksandra.zuchewicz/basics-of-api-testing-using-postman-c14efdf3b8e6
- https://www.sisense.com/blog/rest-api-testing-strategy-what-exactly-should-you-test/
- https://dzone.com/articles/api-testing-is-great-so-why-isnt-everyone-doing-it (archived)
- https://smartbear.com/solutions/api-testing/
- https://www.edureka.co/blog/what-is-api-testing
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