diff --git a/Lib/test/__main__.py b/Lib/test/__main__.py
--- a/Lib/test/__main__.py
+++ b/Lib/test/__main__.py
@@ -1,13 +1,3 @@
-from test import regrtest, support
+from test import regrtest
 
-
-TEMPDIR, TESTCWD = regrtest._make_temp_dir_for_build(regrtest.TEMPDIR)
-regrtest.TEMPDIR = TEMPDIR
-regrtest.TESTCWD = TESTCWD
-
-# Run the tests in a context manager that temporary changes the CWD to a
-# temporary and writable directory. If it's not possible to create or
-# change the CWD, the original CWD will be used. The original CWD is
-# available from support.SAVEDCWD.
-with support.temp_cwd(TESTCWD, quiet=True):
-    regrtest.main()
+regrtest.main_in_temp_cwd()
diff --git a/Lib/test/regrtest.py b/Lib/test/regrtest.py
--- a/Lib/test/regrtest.py
+++ b/Lib/test/regrtest.py
@@ -1543,7 +1543,9 @@
                initial_indent=blanks, subsequent_indent=blanks))
 
 
-def _make_temp_dir_for_build(TEMPDIR):
+def _make_temp_dir_for_build():
+    """Change TEMPDIR for testing if necessary."""
+    global TEMPDIR
     # When tests are run from the Python build directory, it is best practice
     # to keep the test files in a subfolder.  It eases the cleanup of leftover
     # files using command "make distclean".
@@ -1555,13 +1557,24 @@
         except FileExistsError:
             pass
 
+
+def main_in_temp_cwd():
+    """Run main() in a temporary working directory."""
+    _make_temp_dir_for_build()
+
     # Define a writable temp dir that will be used as cwd while running
     # the tests. The name of the dir includes the pid to allow parallel
     # testing (see the -j option).
-    TESTCWD = 'test_python_{}'.format(os.getpid())
+    test_cwd = 'test_python_{}'.format(os.getpid())
+    test_cwd = os.path.join(TEMPDIR, test_cwd)
 
-    TESTCWD = os.path.join(TEMPDIR, TESTCWD)
-    return TEMPDIR, TESTCWD
+    # Run the tests in a context manager that temporary changes the CWD to a
+    # temporary and writable directory. If it's not possible to create or
+    # change the CWD, the original CWD will be used. The original CWD is
+    # available from support.SAVEDCWD.
+    with support.temp_cwd(test_cwd, quiet=True):
+        main()
+
 
 if __name__ == '__main__':
     # Remove regrtest.py's own directory from the module search path. Despite
@@ -1585,11 +1598,4 @@
     # sanity check
     assert __file__ == os.path.abspath(sys.argv[0])
 
-    TEMPDIR, TESTCWD = _make_temp_dir_for_build(TEMPDIR)
-
-    # Run the tests in a context manager that temporary changes the CWD to a
-    # temporary and writable directory. If it's not possible to create or
-    # change the CWD, the original CWD will be used. The original CWD is
-    # available from support.SAVEDCWD.
-    with support.temp_cwd(TESTCWD, quiet=True):
-        main()
+    main_in_temp_cwd()