Merge pull request #547 from realpython/unittest-mock

Add example code for unittest.mock resurfacing

Author: brendaweles

unittest-mock/README.md

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+# Understanding the Python Mock Object Library
+
+This folder contains code examples related to the RealPython tutorial on [Understanding the Python Mock Object Library](https://realpython.com/python-mock-library/).
+
+The example code showcases some of the different use cases of `unittest.mock` in a single test file, `test_my_calendar.py`. When writing your own tests, keep in mind that readability counts and that your test code will be more readable if you keep one consistent approach to mocking.
+
+## Installation
+
+1. Create a Python virtual environment
+
+```sh
+$ python -m venv ./venv
+$ source venv/bin/activate
+(venv) $
+```
+
+2. Install the requirements
+
+```sh
+(venv) $ pip install requests
+```
+
+## Run the Tests
+
+```sh
+(venv) $ python test_my_calendar.py
+```
+
+All the tests should pass. Go ahead and play with the code examples, change them, break them, and practice your understanding of using `unittest.mock` for testing in Python.
+
+## About the Author
+
+Martin Breuss - Email: [email protected]
+
+## License
+
+Distributed under the MIT license. See ``LICENSE`` for more information.

unittest-mock/my_calendar.py

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+from datetime import datetime
+
+import requests
+
+
+def is_weekday():
+    today = datetime.today()
+    # Python's datetime library treats Monday as 0 and Sunday as 6
+    return 0 <= today.weekday() < 5
+
+
+def get_holidays():
+    r = requests.get("http://localhost/api/holidays")
+    if r.status_code == 200:
+        return r.json()
+    return None

unittest-mock/test_my_calendar.py

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+import datetime
+import unittest
+from unittest.mock import Mock, patch
+
+import requests
+from my_calendar import get_holidays, is_weekday
+from requests.exceptions import Timeout
+
+
+class TestCalendar(unittest.TestCase):
+    @classmethod
+    def setUpClass(cls):
+        cls.wednesday = datetime.datetime(year=2025, month=1, day=1)
+        cls.sunday = datetime.datetime(year=2025, month=1, day=5)
+        cls.holidays = {"12/25": "Christmas", "7/4": "Independence Day"}
+        cls.response_setup_dict = {
+            "json.return_value": TestCalendar.holidays,
+            "status_code": 200,
+        }
+
+    def log_request(self, url):
+        """Helper function that logs and returns a mock successful request."""
+        print(f"Making a request to {url}.")
+        print("Request received!")
+        response_mock = Mock(**TestCalendar.response_setup_dict)
+        return response_mock
+
+    @patch("my_calendar.datetime")
+    def test_is_weekday_returns_true_on_weekdays(self, mock_datetime):
+        mock_datetime.today.return_value = TestCalendar.wednesday
+        self.assertTrue(is_weekday())
+
+    @patch("my_calendar.datetime")
+    def test_is_weekday_returns_false_on_weekends(self, mock_datetime):
+        mock_datetime.today.return_value = TestCalendar.sunday
+        self.assertFalse(is_weekday())
+
+    # Example of patching only a specific object
+    @patch.object(requests, "get", side_effect=requests.exceptions.Timeout)
+    def test_get_holidays_timeout(self, mock_requests):
+        with self.assertRaises(requests.exceptions.Timeout):
+            get_holidays()
+
+    # Example of using the `with` statement with `patch()`
+    def test_get_holidays_logging(self):
+        with patch("my_calendar.requests") as mock_requests:
+            mock_requests.get.side_effect = self.log_request
+            self.assertEqual(get_holidays()["12/25"], "Christmas")
+
+    @patch("my_calendar.requests")
+    def test_get_holidays_retry(self, mock_requests):
+        response_mock = Mock(**TestCalendar.response_setup_dict)
+        # Set the side effect of .get()
+        mock_requests.get.side_effect = [Timeout, response_mock]
+        # Test that the first request raises a Timeout
+        with self.assertRaises(Timeout):
+            get_holidays()
+        # Now retry, expecting a successful response
+        self.assertEqual(get_holidays()["12/25"], "Christmas")
+        # Finally, assert .get() was called twice
+        self.assertEqual(mock_requests.get.call_count, 2)
+
+
+if __name__ == "__main__":
+    unittest.main()