human
Solve the following python programming problem given the following code:
# %load test_foo.py
from nose.tools import assert_equal

class TestFoo(object):

    def test_foo(self):
        assert_equal(foo(None), None)
        assert_equal(foo(0), 0)
        assert_equal(foo('bar'), 'bar')
        print('Success: test_foo')

def main():
    test = TestFoo()
    test.test_foo()

if __name__ == '__main__':
    main()
Given the above code, generate some markdown instructions for it.
assistant
#Here is the Python code you requested.

Unit Test
The following unit test is expected to fail until you solve the challenge.