adapt to oslo.log changes

This change refactors prvisep util test cases to account for the
fact that oslo.log now conditionally uses an internal pipe mutex
when logging under eventlet.

This was added by Iac1b0891ae584ce4b95964e6cdc0ff2483a4e57d
which is part of oslo.log 5.3.0

As a result we need to mock all calls to oslo.log in unit tests
that are assertign if os.write is called. when the internal
pipe mutex is used oslo.log calls os.write when the mutex is
released.

Related-Bug: #1983863
Change-Id: Id313669df80f9190b79690fff25f8e3fce2a4aca
(cherry picked from commit ea07f96)

Author: SeanMooney

nova/tests/unit/privsep/test_utils.py

@@ -13,6 +13,7 @@
 #    under the License.
 
 import errno
+import fixtures
 import os
 from unittest import mock
 
@@ -55,6 +56,13 @@ def setUp(self):
         self.mock_close = close_patcher.start()
         self.mock_unlink = unlink_patcher.start()
         random_string_patcher.start()
+        # as of change Iac1b0891ae584ce4b95964e6cdc0ff2483a4e57d in oslo.log
+        # oslo.log will now internally call os.write() in its PipeMutex code.
+        # This causes the mock_write() to be called which breaks some of
+        # the testcases as we expect mock_write() to be called only
+        # by the code under test.
+        self.useFixture(fixtures.MonkeyPatch(
+            "nova.privsep.utils.LOG", mock.Mock()))
 
     def test_supports_direct_io(self):
         self.mock_open.return_value = 3
@@ -85,6 +93,7 @@ def test_supports_direct_io_with_exception_in_write(self):
     def test_supports_direct_io_with_exception_in_open(self):
         self.mock_open.side_effect = ValueError()
 
+        self.mock_open.assert_not_called()
         self.assertRaises(ValueError, nova.privsep.utils.supports_direct_io,
                           '.')