Given a set (i.e., no duplicate) of integer numbers, e.g. [1, 3, 2, 4], write a function that returns all unique subsets of the given set.
- Set A is a subset of a set B if all elements of A are also elements of B.
- It is possible for A and B to be equal.
- It is possible for A and B to be empty.
- By definition, order of elements in a set is not important, e.g., [1, 2] and [2, 1] are considered the same set. The output of the function should contain all unique subsets of the input set, in any order the candidate chooses. Please include the test cases you used for your solution.