test: fix test coverage

Author: kayjan

CHANGELOG.md

@@ -6,7 +6,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 ### Changed
-- Misc: Some code refactoring, enhance assemble_attributes
+- Misc: Some code refactoring, enhance assemble_attributes.
+### Fixed
+- Test: Test for `tree_to_nested_dict_key` for BinaryNode.
+- Error: Check and throw error for `dataframe_to_dag`, previously this error will not have been found out.
 
 ## [0.30.0] - 2025-09-05
 ### Added:

tests/binarytree/test_export.py

@@ -92,6 +92,26 @@ def test_tree_to_nested_dict(binarytree_node):
         assert actual == expected, f"Expected\n{expected}\nReceived\n{actual}"
 
 
+class TestTreeToNestedDictKey:
+    @staticmethod
+    def test_tree_to_nested_dict_key(binarytree_node):
+        expected = {
+            "1": {
+                "children": {
+                    "2": {
+                        "children": {
+                            "4": {"children": {"8": {}}},
+                            "5": {},
+                        },
+                    },
+                    "3": {"children": {"6": {}, "7": {}}},
+                },
+            }
+        }
+        actual = export.tree_to_nested_dict_key(binarytree_node)
+        assert actual == expected, f"Expected\n{expected}\nReceived\n{actual}"
+
+
 class TestTreeToDot:
     @staticmethod
     def test_tree_to_dot(binarytree_node):