I tried giving it one of the prompts from copilot.github.com:

    def strip_suffix(filename):
        """
        Removes the suffix from a filename
        """
        return filename[:filename.rfind('.')]

    def test_strip_suffix():

It completed the test function like this:

        # test stripping of a suffix
        a = strip_suffix("I_am_file.txt")
        assert a == "I_am_file"

Compare this with GitHub Copilot, which gives:

        """
        Tests for the strip_suffix function
        """
        assert strip_suffix('notes.txt') == 'notes'
        assert strip_suffix('notes.txt.gz') == 'notes.txt'

GPT-J also gave a bunch of explanation on how to use the generated code:

    So this goes in a file called my_file.py and when you run python3.4 -m my_file.strip_suffix you should get the following output
    C:\Users\user\Desktop>python3.4 -m my_file.strip_suffix
    'strip_suffix'

    C:\Users\user\Desktop>

    So the strip_suffix function which strips the suffix from a filename is called as part of a larger code that uses some functions from the file. To tell Python what functions are available in a file you just need to put #-comment characters on the first line and then the functions that you want to use, and the first line will be taken as the function documentation:
    #-*- coding: utf-8 -*-
    #comment
    def func_one():
        '''
        Documentation for function one.
        '''
        print("This is the doc for func_one