Rename tests to correspond to use case requirements rather than the methods tested.

[BjoernKW]

Currently, most of the test methods in the sample solution are named like the methods they test, e.g., we have a test method getAllBooks() for testing a controller method getAllBooks().

Something more in line with user requirements, such as endpointShouldReturnAListOfBooks would be more explicit and contribute to a more test-driven approach as well as more explicitly document the desired behaviour.