Let’s say you are testing a software product and you need to decide what kind of end-to-end tests to write so you test the product most efficiently. If you are thinking between API and UI tests it is important to know for which purpose and for what kind of scenarios it is best to use each of them. That will help you to have an optimized testing strategy and more efficient testing.
UI vs. API Tests
When we are writing API (Application Programming Interface) tests, we interact with the application’s API and focus on the data, validations, status codes, and communication between different parts of the app. If we want to write tests with scenarios to check the status codes of the endpoints, the flow of the data through different endpoints, back-end validations, and invalid inputs, or to perform security or performance testing, then the API tests are the right choice. With these tests, our main focus is to check if the back end of the application works properly, and not the user interface.
On the other side, UI (User Interface) testing is focused on the front end of the application, and the tests communicate with the app from the front end by making some actions like a real end user. When we are writing UI tests, we are focused on navigating through the app by clicking on buttons, entering data in the forms, and doing some other actions that a real end user would do on the front end of the application. While we are doing that, we are validating if the elements are shown correctly, whether are they marked with the right color, whether are we navigated on the right page, etc. We can also check how the app behaves on different devices, browsers, operating systems, screen sizes, and resolutions, and how usable the app is.
When to Use API Testing?
You can consider writing API tests in the following situations:
- When the app is at the beginning of the development process, and if the UI is still not developed, we can start by writing an API test to make sure that the back end is working correctly and to catch issues earlier in the development process. After that, when the UI part is developed we will be more confident because we will know that the back end is tested and it is stable.
- When the application is complex and has some calculations, decisions based on the data that is entered, data processing, etc, the API tests are essential. With the API tests, we can validate that all the calculations for example are done properly on the back end, and sometimes we can also validate some things that we are not able to validate on the front end.
- When we are dealing with microservices architectures and distributed systems, different components communicate through APIs. To verify that these components interact correctly, the first option for us is to write API tests.
- Through the API, by using some tools like JMeter, or K6, we can create performance and load tests that will check how well the app can handle high traffic, large data sets, or stress conditions.
- When we want to check the security of the app, we are using API tests, to test authentication, authorization, and data protection mechanisms at the core level. With these tests, we can discover crucial vulnerabilities in the app.
When to Use UI Testing?
- With UI tests, we can test what kind of experience the user has when interacting with the elements and all the validations that can be triggered and seen on the front end.
- With the UI testing, we can make tests that cover the complete end-to-end user flow with all the element interactions, completing forms, etc. With this, we can be sure that the end users can complete their actions on the app and that all the elements are shown correctly.
- With UI tests, we can check how the app behaves on different devices, browsers, operating systems, and screen sizes.
- By testing the app from the UI, we can test how usable and user-friendly it is, and by using it like a real end-user, we can find some issues or suggest some improvements.
- If the application needs to be accessible to users with disabilities, UI testing is vital. It ensures that the interface complies with accessibility standards, providing a user-friendly experience for everyone.
Example Project: Healthcare Management System
Let’s say we are working on a healthcare management system that hospitals use to manage patient records, appointments, and billing. The system includes a back-end that handles patient data, appointment scheduling, and insurance claims, while the front-end provides interfaces for doctors, nurses, and administrative staff to access and update information.
Write API Tests:
- That will create, update, retrieve, and delete patient records.
- To validate that sensitive data, such as medical history, is encrypted and accessible only to authorized users.
- To ensure that the data is processed correctly and securely before it is presented in the UI.
- That will verify that the logic for calculating the time for the doctor’s appointments is working correctly.
- To check the logic for calculating the cost is working correctly based on the provided data.
Write UI Tests:
- That will check scenarios where a doctor logs into the system, navigates to a patient’s record, reviews medical history, and updates notes during an appointment.
- To verify that doctor can access patient information, view their daily schedule, and make notes during consultations.
- To ensure that the interface is easy to navigate, all necessary information is captured, and error messages are shown correctly when there are issues.
- To check that the billing process can be done successfully and without any errors.
As we can see from the example, it is important to have an approach where we will balance the usage of API and UI tests. By integrating both API and UI testing, you can ensure that the system functions correctly from the back end side, but also provides a great experience for the end-users.
