Demonstrating Python3 Unit Testing with MagicMock, patch, and mock_open (open())

test_unique_names.py

"""
Test cases for the unique_names module that includes a context manager
for the open() call.  
"""
import unittest
import unique_names
from unittest.mock import Mock, MagicMock, patch, mock_open


class TestUnique(unittest.TestCase):
    def test_get_names_from_file_open(self):
        # Demonstrate mocking the open() call to read a file.
        # The contents of the file are mocked in this test, providing
        # coverage to the whole reader.
        read_data = 'Jack\nJack\nAmos\n'
        # m = mock_open(read_data=read_data)
        with patch('builtins.open', mock_open(read_data=read_data)) as mock_file:
            names = unique_names.get_names_from_file('filename.txt')
            self.assertEqual(names, ['Jack', 'Jack', 'Amos'])

    def test_unique_names_mm(self):
        #  Demonstrate using MagicMock to test the uniqueness filter
        unique_names.get_names_from_file = MagicMock()
        unique_names.get_names_from_file.return_value = ['Jack', 'Ross', 'Mike', 'Jack', 'Tom', 'Kate', 'Ross']

        names = unique_names.get_unique_names("names.txt")
        self.assertEqual(names, ['Jack', 'Kate', 'Mike', 'Ross', 'Tom'])

    @patch('unique_names.get_names_from_file')
    def test_unique_names_pd(self, mock_get_names_from_file):
        # Demonstrate using patch to test the uniqueness filter. Patch
        # is used as a decorator.
        mock_get_names_from_file.return_value = ['Jack', 'Ross', 'Mike', 'Jack', 'Tom', 'Kate', 'Ross']

        names = unique_names.get_unique_names("names.txt")
        self.assertEqual(names, ['Jack', 'Kate', 'Mike', 'Ross', 'Tom'])
        
    def test_unique_names_pcm(self):
        # Demonstrate using patch as a context manager (with block)
        with patch('unique_names.get_names_from_file') as mock_get_names_from_file:
            mock_get_names_from_file.return_value = ['Jack', 'Ross', 'Mike', 'Jack', 'Tom', 'Kate', 'Ross']

            names = unique_names.get_unique_names("names.txt")
            self.assertEqual(names, ['Jack', 'Kate', 'Mike', 'Ross', 'Tom'])

if __name__ == "__main__":
    unittest.main()

unique_names.py

def get_names_from_file(filename):
    with open(filename, "r") as f:
        lines = f.readlines()
        names = []

        for line in lines:
            names.append(line.strip())

        return names

def get_unique_names(filename):
    names = get_names_from_file(filename)
    unique_names = list(set(names))
    return sorted(unique_names)

if __name__ == "__main__":
    print(get_unique_names("names.txt"))
    

$ python3 -m unittest -v test_unique_names.py 
test_get_names_from_file_open (test_unique_names.TestUnique.test_get_names_from_file_open) ... ok
test_unique_names_mm (test_unique_names.TestUnique.test_unique_names_mm) ... ok
test_unique_names_pcm (test_unique_names.TestUnique.test_unique_names_pcm) ... ok
test_unique_names_pd (test_unique_names.TestUnique.test_unique_names_pd) ... ok

----------------------------------------------------------------------
Ran 4 tests in 0.003s

OK

# duplicates are: Taylor, Jordan 
$ echo -e "Alex\nTaylor\nJordan\nEmily\nCasey\nTaylor\nAaliyah\nJordan\nJamie\nTaylor" > names.txt
$ python3 unique_names.py 
['Aaliyah', 'Alex', 'Casey', 'Emily', 'Jamie', 'Jordan', 'Taylor']