All tests in ContactManagerImplTest can now run independently
Deleted unnecessary lines of code.
Tidied up tests, and rearranged (where necessary) to ensure each test can run independently
Tidied up to make code look a little clearer
created new test for flush method
wrote minimum code for flush method to pass current test.
New test for flush() method now tests file content exists
written minimum code for flush() method to pass current test
tidied up test code
Now tests if data files created by flush method contains objects with any content
Corrected lines testing that AtomicNumber objects in flushed data file are not just new obejcts
Added new tests for flush() method to ensure objects in data file contain the correct content
flush() method in ContactManagerImpl now passes all tests
Written tests to ensure data file is read by constructor method
Constructor method currently thinks the data file always exists.
added tearDown() method to test, added shutdownHook to ContactManagerImpl

The tearDown method deletes the data file after each test, fixing the problem I was having in the last commit.