diff --git a/setup.cfg b/setup.cfg
index 45ebfe3..1c8f5fb 100644
--- a/setup.cfg
+++ b/setup.cfg
@@ -64,7 +64,7 @@ zip_safe = False
 #   bin/second.py
 
 install_requires =
-    # snazzy
+    typing-extensions;python_version<'3.11'
 
 # [options.package_data]
 # * = *.txt, *.rst
diff --git a/tests/test_fs.py b/tests/test_fs.py
index 49a2c94..1f54c8b 100644
--- a/tests/test_fs.py
+++ b/tests/test_fs.py
@@ -14,32 +14,6 @@
 
 
 class TestFS:
-    # @pytest.mark.skipif(os.name == "nt", reason="windows has different eol size")
-    # def test_fs_linux(self):
-    #     path = Path(__file__).parent / "fixtures"
-
-    #     # We check for unix line endings/file sizes (as used on travis)
-    #     tree = load_tree_from_fs(path)
-    #     assert fixture.check_content(
-    #         tree,
-    #         """
-    #         FileSystemTree<*>
-    #         ├── 'file_1.txt', 13 bytes, 2022-04-14 21:35:21
-    #         ╰── [folder_1]
-    #             ╰── 'file_1_1.txt', 15 bytes, 2022-04-14 21:35:21
-    #         """,
-    #     )
-
-    #     tree = load_tree_from_fs(path, sort=False)
-    #     assert "[folder_1]" in fixture.canonical_repr(tree)
-
-    # @pytest.mark.skipif(os.name != "nt", reason="windows has different eol size")
-    # def test_fs_windows(self):
-    #     path = Path(__file__).parent / "fixtures"
-    #     # Cheap test only,
-    #     tree = load_tree_from_fs(path)
-    #     assert "[folder_1]" in fixture.canonical_repr(tree)
-
     def test_fs_serialize(self):
         KEEP_FILES = False
         path = Path(__file__).parent / "fixtures"
@@ -69,3 +43,36 @@ def test_fs_serialize_unsorted(self):
         tree = load_tree_from_fs(path, sort=False)
         assert "[folder_1]" in fixture.canonical_repr(tree)
         assert len(tree) == 3
+
+    # NOTE: these tests are not very useful, since they depend on the file system
+    # and the file system is not under our control (e.g. line endings, file sizes, etc.)
+    # Especially on GitHub Actions we have no control over the file system and
+    # timestamps, so we cannot compare the output of `load_tree_from_fs` with a
+    # fixture.
+    # We should only test the serialization/deserialization here.
+
+    # @pytest.mark.skipif(os.name == "nt", reason="windows has different eol size")
+    # def test_fs_linux(self):
+    #     path = Path(__file__).parent / "fixtures"
+
+    #     # We check for unix line endings/file sizes (as used on travis)
+    #     tree = load_tree_from_fs(path)
+    #     assert fixture.check_content(
+    #         tree,
+    #         """
+    #         FileSystemTree<*>
+    #         ├── 'file_1.txt', 13 bytes, 2022-04-14 21:35:21
+    #         ╰── [folder_1]
+    #             ╰── 'file_1_1.txt', 15 bytes, 2022-04-14 21:35:21
+    #         """,
+    #     )
+
+    #     tree = load_tree_from_fs(path, sort=False)
+    #     assert "[folder_1]" in fixture.canonical_repr(tree)
+
+    # @pytest.mark.skipif(os.name != "nt", reason="windows has different eol size")
+    # def test_fs_windows(self):
+    #     path = Path(__file__).parent / "fixtures"
+    #     # Cheap test only,
+    #     tree = load_tree_from_fs(path)
+    #     assert "[folder_1]" in fixture.canonical_repr(tree)
diff --git a/tests/test_typing_concept.py b/tests/test_typing_concept.py
index 96c8c6d..710d413 100644
--- a/tests/test_typing_concept.py
+++ b/tests/test_typing_concept.py
@@ -2,40 +2,40 @@
 
 from __future__ import annotations
 
-import pytest
-
-# pytest.skip(allow_module_level=True)
+from typing import Any, Generic, List, Type, TypeVar, cast
 
 try:
-    from typing import Any, Generic, List, Self, TypeVar, cast
+    from typing import Self
 except ImportError as e:
     print(f"ImportError: {e}")
+    from typing_extensions import Self
+    # _ = pytest.importorskip("typing_extensions")
     # from typing_extensions import Self
-    typing_extensions = pytest.importorskip("typing_extensions")
-    Self = typing_extensions.Self
 
 
 # TData = TypeVar("TData")
 TNode = TypeVar("TNode", bound="Node")
 
 
-class Node:
-    def __init__(self, data: Any, parent: Node):
+class Node(Generic[TNode]):
+    def __init__(self, data: Any, parent: Self):
         self.data: Any = data
-        self.parent: Node = parent
-        self.children: List[Node] = []
+        self.parent: Self = parent
+        self.children: List[Self] = []
 
-    def add(self, data: Any) -> Node:
-        node = Node(data, self)
+    def add(self, data: Any) -> Self:
+        node = self.__class__(data, self)
         self.children.append(node)
         return node
 
 
 class Tree(Generic[TNode]):
+    node_class: Type[TNode] = Node
+
     def __init__(self):
-        self.root: Node = Node("__root__", cast(TNode, None))
+        self.root: TNode = self.node_class("__root__", cast(TNode, None))
 
-    def add(self, data: Any) -> Node:
+    def add(self, data: Any) -> TNode:
         node = self.root.add(data)
         return node
 
@@ -44,26 +44,27 @@ def first(self) -> TNode:
 
 
 # ----------------------------
-# ----------------------------
 
 
 class TypedNode(Node):
-    def __init__(self, data: Any, kind: str, parent: TypedNode):
+    def __init__(self, data: Any, kind: str, parent: Self):
         super().__init__(data, parent)
         self.kind: str = kind
         # self.children: List[TypedNode] = []
 
-    def add(self, data: Any, kind: str) -> TypedNode:
-        node = TypedNode(data, kind, self)
+    def add(self, data: Any, kind: str) -> Self:
+        node = self.__class__(data, kind, self)
         self.children.append(node)
         return node
 
 
 class TypedTree(Tree[TypedNode]):
+    node_class = TypedNode
+
     def __init__(self):
         self.root: TypedNode = TypedNode("__root__", "__root__", cast(TypedNode, None))
 
-    def add(self, data: Any, kind: str) -> TNode:
+    def add(self, data: Any, kind: str) -> TypedNode:
         node = self.root.add(data, kind)
         return node
 
diff --git a/tox.ini b/tox.ini
index d632e32..25f92ad 100644
--- a/tox.ini
+++ b/tox.ini
@@ -29,6 +29,8 @@ deps =
     pytest-cov
     pytest-html
     rdflib
+    # py39: typing-extensions>=4.0
+    # py310: typing-extensions>=4.0
 setenv =
     COVERAGE_FILE=.coverage.{envname}
 ; allowlist_externals =