What is the difference between unit and integration tests?

Unit tests and integration tests differ in their level of verification and purpose:

• Unit tests check individual components or methods in isolation from the rest of the system. They are fast, help identify errors early, and usually use mocks for dependencies.

• Integration tests verify the interaction between multiple components or subsystems. They ensure that modules work correctly together and often require a real environment or database.

Example:

• A unit test checks a method that calculates the sum of two numbers.
• An integration test verifies that a service correctly saves data to a database and returns the expected result.

Thus, unit tests focus on internal logic, while integration tests focus on component interaction.