Spring brings a few options in order to test web applications, and most Spring developers are familiar with them, these are:

MockMvc: Mocks the servlet API, useful for non-reactive web apps

TestRestTemplate: Can be used pointing to our app, useful for non-reactive web apps where mocked servlets are not desirable

WebTestClient: Is a testing tool for reactive web apps, both with mocked requests/responses or hitting a real server

Using profiles wisely – how profiles impact performance

Reconsidering @MockBean – how mocking hits performance

Refactoring @MockBean – alternatives to improve performance

Thinking carefully about @DirtiesContext – a useful but dangerous annotation and how not to use it

Using test slices – a cool tool that can help or get on our way

Using class inheritance – a way to organize tests in a safe manner

State management – good practices to avoid flakey tests

Refactoring into unit tests – the best way to get a solid and snappy build

https://www.baeldung.com/spring-tests