Make the test helpers more correct on their own.

2 files changed, 8 insertions, 6 deletions

diff --git a/coverage/test_helpers.py b/coverage/test_helpers.py
index efe68dcd..082fc15e 100644
--- a/coverage/test_helpers.py
+++ b/coverage/test_helpers.py
@@ -132,8 +132,13 @@ class StdStreamCapturingMixin(TestCase):
         return self.captured_stderr.getvalue()
 
 
-class TempDirMixin(TestCase):
-    """A test case mixin that creates a temp directory and files in it."""
+class TempDirMixin(SysPathAwareMixin, ModuleAwareMixin, TestCase):
+    """A test case mixin that creates a temp directory and files in it.
+
+    Includes SysPathAwareMixin and ModuleAwareMixin, because making and using
+    temp dirs like this will also need that kind of isolation.
+
+    """
 
     # Our own setting: most of these tests run in their own temp directory.
     run_in_temp_dir = True
diff --git a/tests/coveragetest.py b/tests/coveragetest.py
index 19fc0612..a680ed46 100644
--- a/tests/coveragetest.py
+++ b/tests/coveragetest.py
@@ -8,8 +8,7 @@ from coverage.backward import StringIO, import_local_file
 from coverage.backward import importlib     # pylint: disable=unused-import
 from coverage.control import _TEST_NAME_FILE
 from coverage.test_helpers import (
-    ModuleAwareMixin, SysPathAwareMixin, EnvironmentAwareMixin,
-    StdStreamCapturingMixin, TempDirMixin,
+    EnvironmentAwareMixin, StdStreamCapturingMixin, TempDirMixin,
 )
 
 from tests.backtest import run_command
@@ -19,8 +18,6 @@ from tests.backtest import run_command
 OK, ERR = 0, 1
 
 class CoverageTest(
-    ModuleAwareMixin,
-    SysPathAwareMixin,
     EnvironmentAwareMixin,
     StdStreamCapturingMixin,
     TempDirMixin,