Why every Frontend Developer Needs to Understand Unit, Integration, End-to-End, and Acceptance Testing

Testing your frontend code is just as important as writing it. Without tests, it becomes increasingly difficult to ensure that your application remains stable and provides the expected behavior. In this article, we will discuss four types of testing that every frontend developer should understand: Unit, Integration, End-to-End, and Acceptance.

Unit Testing

Unit testing is the process of testing a particular unit of code in isolation. A unit can be anything from a function to a component. The goal of unit testing is to ensure that each unit of code behaves as expected in all possible scenarios.

For example, let's think about an aviation app. We can create a unit test for a function that converts measurement units. This function should receive a value in a specific unit and return the equivalent to another unit that the user selects. This test should consider different values, such as converting from kilometers to miles or gallons to liters, among others. The test will validate if the function is providing the expected values correctly.

To perform unit testing, a developer uses testing frameworks such as Jest, Mocha, or Jasmine. With these frameworks, it's possible to write test suites with multiple test cases to cover all possible scenarios that a specific unit of code can face.

Integration Testing

Integration testing involves testing the integration of multiple units of code to ensure they work together correctly. Integration tests help to find defects early in the development cycle that a unit test may not catch. It is crucial to verify that multiple units of code can collaborate in an application without errors.

Let's continue using the aviation app example. We can create an integration test to verify if the function responsible for calculating flight time is correctly connected to the function that calculates the fuel consumption per hour. Both functions should work together in an integrated way to calculate the estimated flight duration based on the fuel consumption of the aircraft.

Integration tests tend to be more complex and involve more setup than unit tests. Developers need to understand the full system, including all the units that will collaborate in a particular scenario. The tests also require different test environments and configurations to closely replicate real-world scenarios.

End-to-End Testing

End-to-End testing is a comprehensive test that verifies if an entire application flows correctly and provides the expected results. Starting at the user interface, E2E testing simulates real-world user scenarios. The goal is to ensure that all the units of code, APIs, and third-party services work together correctly.

Using the aviation app, we can create an end-to-end test that simulates a user making a flight reservation. This test should ensure that the entire flow of the application works correctly from start to finish, including login, selecting the flight, payment processing, and sending a confirmation email to the user's address.

End-to-End tests require more infrastructure and have longer execution times since it involves all parts of the application. Developers need to carefully select which tests to execute and keep them as lean and minimal as possible.

Acceptance Testing

Acceptance testing is the process of verifying that the application meets the user's requirements. Acceptance tests aim to validate the entire user experience, covering both functional and non-functional aspects of the application.

Still following the aviation app, let's suppose that the user needs a form to reserve a flight. The form should allow the user to input personal and payment information to complete the reservation. An acceptance test should validate that the form appears correctly, the user can input all necessary information, and the server receives the right information to calculate the payment.

Acceptance tests should be written in collaboration with the application stakeholders, such as product owners, quality assurance, and designers. Involving all stakeholders helps to ensure that the acceptance tests reflect the user's needs and expectations.

Conclusion

Frontend testing is a fundamental part of the development process. Unit, Integration, End-to-End, and Acceptance tests have different scopes but aim to ensure the quality, stability, and performance of the application.

Developers need to understand the differences between each type of test and when to use one over the other. Different testing frameworks, such as Jest, Cypress, and Playwright, can facilitate writing and running tests in a programmatic way.

Automated testing is not enough to ensure a perfect product, but it helps to detect defects early in the development cycle, making it easier and less expensive to fix them. Encouraging a culture of continuous testing helps developers and testers to work together, share knowledge, and learn from experience to deliver an error-free product for their users.