What’s the difference between Unit, Integration, and End-to-End tests? 🤔

In software development, testing is crucial to ensuring our code works as expected in different scenarios. But with various types of tests available, it’s important to understand their specific purpose and when to use each one.

I’ve put together this animation using a car 🚗 as an analogy to explain these concepts:

𝐔𝐧𝐢𝐭 𝐓𝐞𝐬𝐭𝐬:

Unit tests focus on “units of behavior,” such as a function or class, isolated from the rest of the system. They run quickly and help catch issues early. In the animation, the car frame is tested in isolation (e.g., how comfortable or durable it is) by using test-doubles for other components like the wheels and headlights. 

𝐈𝐧𝐭𝐞𝐠𝐫𝐚𝐭𝐢𝐨𝐧 𝐓𝐞𝐬𝐭𝐬:

Integration tests check how different components work together. For example, you could test the communication between a service and a database 🗄️. In the animation, integration testing combines the car frame, wheels, and headlights to ensure these parts interact properly.

𝐄𝐧𝐝-𝐭𝐨-𝐄𝐧𝐝 (𝐄𝟐𝐄) 𝐓𝐞𝐬𝐭𝐬:

E2E tests simulate real user interactions by testing the entire system—from the user interface to the back-end. These tests catch issues that unit and integration tests might miss 🕵️. In the animation, the car is fully assembled and taken on a drive to ensure everything works together as expected.

Each type of test has a unique role, and together they provide the comprehensive coverage needed to ensure your code is reliable, maintainable, and ready for real-world usage.