SpringBoot Simplify AssertJ assertions and also make them more readable

Simplified AssertJ assertions (e.g. instead of doing assertThat(list.size()).isEqualTo(2) one can do assertThat(list).hasSize(2) which provides cleaner error message and makes the test slightly more readable). Change was mostly automated using "Concise AssertJ Optimizing Nitpicker ​(Cajon)​", with some manual work where it made incorrect changes.

Comment From: philwebb

Nice work! Thanks.

Comment From: mhalbritter

Thank you and congratulations to your first Spring Boot contribution!