Tell me three real numbers that are equal to their cubes?
Might be a good idea to change the test suite to "assert(isequal(cube3(),cube3().^3))" so that the answer isn't revealed by looking at the test suite.
Michael C. had a good point, but you also need "assert(numel(unique(cube3()))==3)"
Yo may need to check for length 3
Add a test to assert that length == 3.
It would be a good idea to check that a length 3 vector is returned.