For speed improvements you can test with known arrays with either presorted answers to check against or simply run through the returned array ra checking ra[n] =< ra[n+1] for all n in the range 0..len(ra-1) complexity of which is very low. You can determine if every element is present in each array by counting the instances of each value and then comparing the counts.

Your testing should also include corner cases such as ar=[1] and ar=[] and for an interview I would at least mention testing for invalid inputs such as arrays of non-integer values, non-arrays, etc.

For speed improvements you can test with known arrays with either presorted answers to check against or simply run through the returned array ra checking ra[n] =< ra[n+1] for all n in the range 0..len(ra-1) complexity of which is very low. You can determine if every element is present in each array by counting the instances of each value and then comparing the counts.

Your testing should also include corner cases such as ar=[1] and ar=[] and for an interview I would at least mention testing for invalid inputs such as arrays of non-integer values, non-arrays, etc., I know that the behaviour in such cases is undefined in the case you were given but a part of a testers job is to highlight specification omissions and ambiguities such as what is the error handling. If you only test for what is specifically in the specification you will not make a good tester and this sort of issue is one of the things that the interviewer will be looking for.