display ci build status in README
uncomment BooksIntegrationTest to start fixing
use indentation size 4 instead of 3
remove undefined methodcall in AfterClass
use org.juni.Assert instead of deprecated junit.framework.Assert
fix testListBooks Test by creating a Book first
refactor creation of test book
use Before After instead of BeforeClass AfterClass

To remove state between the Tests
change bookId to non-static
fix testDeleteBook
change books map to public for testing purposes
clear books map in tearDown
fix testUpdateBook
fix testGetUpdatedBook
delete commented out code
refactor by extracting methods
remove println in testListBooks
style tests with empty lines
use lambda syntax for the filters in setup
refactor test method names