title: How to assert that exactly the expected elements are in a list?
body: <p>I want to unit-test a function that takes a list and returns (a very different) list. I know what elements I expect, but I do not know in what order they will me in the returned list. How can I assert that exactly those elements are in the list an no other? I would like to do this using py.test. Also: I expect to have multiple duplicates.</p>