Python: Creating a mock or fake directory with files for unittesting

Question

I am trying to create a unit test for the following function:

def my_function(path):
    #Search files at the given path
    for file in os.listdir(path):
           


        

Answer 1

First of all, you forgot to pass the mocked object to test function. The right way to use mock in your test should be like this.

@mock.patch('my_module.os')
def test_my_function(self, mock_path):

Anyway, you shouldn't mock the endswith, but the listdir. The snippet below is an example and may help you.

app.py

def check_files(path):
    files = []
    for _file in os.listdir(path):
        if _file.endswith('.json'):
            files.append(_file)
    return files

test_app.py

import unittest
import mock
from app import check_files


class TestCheckFile(unittest.TestCase):

    @mock.patch('app.os.listdir')
    def test_check_file_should_succeed(self, mock_listdir):
        mock_listdir.return_value = ['a.json', 'b.json', 'c.json', 'd.txt']
        files = check_files('.')
        self.assertEqual(3, len(files))

    @mock.patch('app.os.listdir')
    def test_check_file_should_fail(self, mock_listdir):
        mock_listdir.return_value = ['a.json', 'b.json', 'c.json', 'd.txt']
        files = check_files('.')
        self.assertNotEqual(2, len(files))

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

Edit: Answering your question in comment, you need to mock the json.loads and the open from your app.

@mock.patch('converter.open')
@mock.patch('converter.json.loads')
@mock.patch('converter.os.listdir')
def test_check_file_load_json_should_succeed(self, mock_listdir, mock_json_loads, mock_open):
    mock_listdir.return_value = ['a.json', 'file_im_looking_for.json', 'd.txt']
    mock_json_loads.return_value = [{"name": "test_json_file", "type": "General"}]
    files = check_files('.')
    self.assertEqual(1, len(files))

But remember! If your is too broad or hard to maintain, perhaps refactoring your API should be a good idea.