added unit tests for unsupported methods of test client
added unit tests for json encoding
added unit test for setting apikey header name
added unit test for getting the response code if no request was send
added test case for response status code and fixed implementation
added unit tests for abstract api and attachment api
added test case for custom fields
Merge pull request #67 from JanMalte/unittests

added some more Unittests
added unit tests for custom fields
fixed missing implementation of
added test for IssuePriority API
added test case for news
added test case for queries
added test case for time entry activities
added tests for group API
fixed missing implementation of
added tests for group API
added some first tests for issue api
added some first tests for issue categories api
added tests for issue relation API