Implement and test the root property

pyiron_workflow/node.py

@@ -317,6 +317,11 @@ def parent(self, new_parent: Composite | None) -> None:
             "parent"
         )
 
+    @property
+    def root(self) -> Node:
+        """The parent-most node in this graph."""
+        return self if self.parent is None else self.parent.root
+
     @property
     def readiness_report(self) -> str:
         input_readiness = "\n".join(

tests/unit/test_composite.py

@@ -590,6 +590,34 @@ def test_de_activate_strict_connections(self):
             msg="Activating should propagate to children"
         )
 
+    def test_root(self):
+        top = AComposite("topmost")
+        top.middle_composite = AComposite("middle_composite")
+        top.middle_composite.deep_node = Composite.create.SingleValue(plus_one)
+        top.middle_function = Composite.create.SingleValue(plus_one)
+
+        self.assertIs(
+            top,
+            top.root,
+            msg="The parent-most node should be its own root."
+        )
+        self.assertIs(
+            top,
+            top.middle_composite.root,
+            msg="The parent-most node should be the root."
+        )
+        self.assertIs(
+            top,
+            top.middle_function.root,
+            msg="The parent-most node should be the root."
+        )
+        self.assertIs(
+            top,
+            top.middle_composite.deep_node.root,
+            msg="The parent-most node should be the root, recursively accessible from "
+                "all depths."
+        )
+
 
 if __name__ == '__main__':
     unittest.main()

tests/unit/test_node.py

@@ -344,6 +344,14 @@ def test_run_after_init(self):
             msg="With run_after_init, the node should run right away"
         )
 
+    def test_root(self):
+        n = ANode("n")
+        self.assertIs(
+            n,
+            n.root,
+            msg="Lone nodes should be their own root, as there is no parent above."
+        )
+
 
 if __name__ == '__main__':
     unittest.main()