hacking: force explicit import of python's mock

Since we dropped support for python 2 [1], we no longer need to use the
mock library, which existed to backport py3 functionality into py2.
Change Ib44b5bff657c8e76c4f701e14d51a4efda3f6d32 cut over to importing
the stock mock, which must be done by saying::

    from unittest import mock

...because if you say::

    import mock

...you will be using the third party mock library instead, which may or
may not be installed.

This commit adds hacking check N371 to enforce the former.

[1] https://review.opendev.org/#/c/687954/

Change-Id: I71439580e80d33cff62aba807df2b35164a47cbe

1 files changed, 13 insertions, 0 deletions

diff --git a/nova/tests/unit/test_hacking.py b/nova/tests/unit/test_hacking.py
index 0cf83abacb..10b2a79db4 100644
--- a/nova/tests/unit/test_hacking.py
+++ b/nova/tests/unit/test_hacking.py
@@ -1030,3 +1030,16 @@ class HackingTestCase(test.NoDBTestCase):
         """
         errors = [(x + 1, 0, 'N370') for x in range(4)]
         self._assert_has_errors(code, checks.check_six, expected_errors=errors)
+
+    def test_import_stock_mock(self):
+        self._assert_has_errors(
+            "import mock",
+            checks.import_stock_mock, expected_errors=[(1, 0, 'N371')])
+        self._assert_has_errors(
+            "from mock import patch",
+            checks.import_stock_mock, expected_errors=[(1, 0, 'N371')])
+        code = """
+                    from unittest import mock
+                    import unittest.mock
+               """
+        self._assert_has_no_errors(code, checks.import_stock_mock)