Revert "Remove importlib-metadata and importlib-resources"

This reverts commit 38435ae81c.

lib/importlib_resources/tests/test_custom.py

@@ -0,0 +1,45 @@
+import unittest
+import contextlib
+import pathlib
+
+import importlib_resources as resources
+from ..abc import TraversableResources, ResourceReader
+from . import util
+from ._compat import os_helper
+
+
+class SimpleLoader:
+    """
+    A simple loader that only implements a resource reader.
+    """
+
+    def __init__(self, reader: ResourceReader):
+        self.reader = reader
+
+    def get_resource_reader(self, package):
+        return self.reader
+
+
+class MagicResources(TraversableResources):
+    """
+    Magically returns the resources at path.
+    """
+
+    def __init__(self, path: pathlib.Path):
+        self.path = path
+
+    def files(self):
+        return self.path
+
+
+class CustomTraversableResourcesTests(unittest.TestCase):
+    def setUp(self):
+        self.fixtures = contextlib.ExitStack()
+        self.addCleanup(self.fixtures.close)
+
+    def test_custom_loader(self):
+        temp_dir = self.fixtures.enter_context(os_helper.temp_dir())
+        loader = SimpleLoader(MagicResources(temp_dir))
+        pkg = util.create_package_from_loader(loader)
+        files = resources.files(pkg)
+        assert files is temp_dir