Adding tests for expected reponse when passing invalid values to Map.get

Adding tests for expected reponse when passing invalid values to Map.get
* These are currently @broken
* Map.get should (as documented) handle an object for multiple or a string for a single selection and return the value(s). Right now, however, the function returns the values object if the first two if-cases are not matched. It needs an additional check to verify that there are indeed no arguments passed.
* Adding comments in the test suite