Unit testing

Unit testing tests one unit of functionality and it keeps dependencies minimal and isolated from the environment, including Spring. We can use simplified alternatives for dependencies such as stubs and/or mocks.

In unit testing, there must not be any external dependencies, because external dependencies aren't available since we are testing a unit. So, remove links with dependencies. The test shouldn't fail because of external dependencies. You can remove external dependencies of your implementation for testing purposes by using stubs and mocks. Stubs create a simple test implementation and a mock dependency class generated at startup-time using a mocking framework.

Let's see the following diagram related to the unit testing example:

Here, you can see both modes of your application, the production mode and unit test mode. In the production mode, the Spring Framework injects dependencies by using the Spring configuration, but in the unit testing mode, Spring doesn't have any role...