simplified containsContain method
Added test for getContacts with null parameter
Added test for getContacts where parameter is not null. Also corrected the test where the parameter is null as was getting error message - call to getContacts is ambiguous as one getContacts takes ints, the other takes a String. So need to pass a null String for it to know what method is being referred to
Added implementation for getContacts(). Test passes as expected. NullPointerException test is however throwing an assertionErrorException
Added line of code to throw NullPointerException when paramater is null. Junit test now passes as expected
Added an extra junit test for when no contact in the contactSet contain the String passes into getContacts
Added tests for getContact() where ID is given as parameter. Tests fail as expected
Added implementation for getContacts(int...ids) and tests now work as expected