unittest patch

from unittest.mock import patch

• patch THE FILE IT'S USED IN, not where it's defined
  • the file only knows about what files are exported
  • Min 7:15 of video
  • Lisa Roach - Demystifying the Patch Function - PyCon 2018
• 3 ways of patching
  • How to use Python's unittest.mock.patch

@patch("path.where.fn_is_used.fn", autospec=True, spec_set=True)
class TestStuff(ApiTestCase):
    def test_stuff(self, mock_my_function):

You can also use your own function

@patch("function.path", MagicMock())
@patch("function.path", return_value=True)
@patch("function.path", my_mock_function)

[patch Arguments]

Lisa Roach - Demystifying the Patch Function - PyCon 2018

Min 19:20

• spec: doesn't know about attributes of attributes
  • should always at least spec
• autospec doesn't know about dynamically created attributes
  • example: class attributes
  • work around: set the attribute that exists
  • can be dangerous because it can trigger code on introspection
  • slows down tests 🐌
• spec_set=True prevent setting properties that don't exist
• new_callable=MagicMockis the default
  • new_callable=PropertyMock
• kwargs
  • `return_value="lisa"
  • name="lisa"
• patch.object
• patch.dict

• patch.multiple

• https://youtu.be/ww1UsGZV8fQ?t=889

-@patch("path.where.fn1")
-@patch("path.where.fn2")
-@patch("path.where.fn3")
class TestStuff(ApiTestCase):
+    def setUp(self):
+        mock_fn1 = patch("path.where_fn1").start()
+        mock_fn2 = patch("path.where_fn2").start()
+        mock_fn3 = patch("path.where_fn3").start()
+        self.addCleanup(patch.stopall)
-    def test_stuff(self, mock_fn1, mock_fn2, mock_fn3):
+    def test_stuff(self):
        ...
-    def test_stuff2(self, mock_fn1, mock_fn2, mock_fn3):
+    def test_stuff2(self):
        ...

• You need mock_check_output because the decorator adds it
  • what does it do???????????

patch for as little as possible, especially for

or use setUp() and tearDown()

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Last update: 2023-04-24