Python Unit Test Not Running in Terminal

I'm working through basic unit testing in Python and have this so far:

import unittest
from mycode import *

class MyFirstTests(unittest.TestCase):
    def test_hello(self):
       self.assertEqual(hello_world(), 'hello world')

The function hello_world() is from the mycode import. When trying to run the test in Terminal, Terminal only returns a new command line prompt but no test results. This is the outcome I want to see:

F
====================================================================
FAIL: test_hello (__main__.MyFirstTests)
--------------------------------------------------------------------
Traceback (most recent call last):
File "mytests.py", line 7, in test_hello
self.assertEqual(hello_world(), 'hello world')
AssertionError: None != 'hello world'
--------------------------------------------------------------------
Ran 1 test in 0.000s
FAILED (failures=1)

What am I doing wrong? Thanks!