fix test pollution of sys.modules

Author: asottile

testing/_py/test_local.py

@@ -2,6 +2,7 @@
 import os
 import sys
 import time
+from unittest import mock
 
 import pytest
 from py import error
@@ -978,6 +979,11 @@ def test_error_preservation(self, path1):
 
 
 class TestImport:
+    @pytest.fixture(autouse=True)
+    def preserve_sys_modules(self):
+        with mock.patch.dict(sys.modules):
+            pass
+
     def test_pyimport(self, path1):
         obj = path1.join("execfile.py").pyimport()
         assert obj.x == 42

testing/test_pathlib.py

@@ -91,6 +91,11 @@ def path1(self, tmp_path_factory: TempPathFactory) -> Generator[Path, None, None
         yield path
         assert path.joinpath("samplefile").exists()
 
+    @pytest.fixture(autouse=True)
+    def preserve_sys_modules(self):
+        with unittest.mock.patch.dict(sys.modules):
+            yield
+
     def setuptestfs(self, path: Path) -> None:
         # print "setting up test fs for", repr(path)
         samplefile = path / "samplefile"