Comment by dragonwriter

> Essentially, you're testing that "my_sort" returns the same as python's standard "sort". Of course, this means you need a second function that acts the same as the function you wrote. In real life, if you had that you probably wouldn't have written the function "my_sort" at all.

You don't need that, that’s just a convenient shortcut when you do have a function that does that (but, I would argue, a not-great example for precisely that reason.)

All you actually need is the ability to verify the property (or set of properties) that you are testing in the output. You could replace the test in that sample with something like this, which I think is a better illustration of what is going on (this is somewhat simplified, rather than the length test you really want to test that it has the same set:

  @given(st.lists(st.integers() | st.floats()))
  def test_sort_correct(lst):
    result = my_sort(lst)
    
    # result has the same unique items as original list
    assert set(result) | set(lst) 

    # for each item, result has the same number of copies as original
    assert all(
      result.count(item) == lst.count(item)
      for item in set(result)
    ) 

    # result is sorted
    assert all(result[n] <= result[n+1] for n in range(len(result)-1))