Fix test failures on older Pythons with os_helper shim. Copied 'from_…

…test_support' from importlib_resources.

setup.cfg

@@ -37,6 +37,7 @@ testing =
 	pyfakefs
 	flufl.flake8
 	pytest-perf >= 0.9.2
+	jaraco.collections
 
 docs =
 	# upstream

tests/fixtures.py

@@ -9,7 +9,7 @@
 import functools
 import contextlib
 
-from .py39compat import FS_NONASCII
+from .py39compat import os_helper
 
 from . import _path
 from ._path import FilesSpec
@@ -335,7 +335,9 @@ def record_names(file_defs):
 
 class FileBuilder:
     def unicode_filename(self):
-        return FS_NONASCII or self.skip("File system does not support non-ascii.")
+        return os_helper.FS_NONASCII or self.skip(
+            "File system does not support non-ascii."
+        )
 
 
 def DALS(str):

tests/py39compat.py

@@ -1,4 +1,18 @@
+import types
+
+from jaraco.collections import Projection
+
+
+def from_test_support(*names):
+    """
+    Return a SimpleNamespace of names from test.support.
+    """
+    import test.support
+
+    return types.SimpleNamespace(**Projection(names, vars(test.support)))
+
+
 try:
-    from test.support.os_helper import FS_NONASCII
+    from test.support import os_helper  # type: ignore
 except ImportError:
-    from test.support import FS_NONASCII  # noqa
+    os_helper = from_test_support('FS_NONASCII', 'skip_unless_symlink')

tests/test_main.py

@@ -5,7 +5,7 @@
 import importlib
 import importlib_metadata
 import contextlib
-from test.support import os_helper
+from .py39compat import os_helper
 
 import pyfakefs.fake_filesystem_unittest as ffs