diff --git a/tests/TreeView/toHierarchy.test.ts b/tests/TreeView/toHierarchy.test.ts
index 66f946c1..666ed0a7 100644
--- a/tests/TreeView/toHierarchy.test.ts
+++ b/tests/TreeView/toHierarchy.test.ts
@@ -1,4 +1,4 @@
-import { toHierarchy } from "../../src/utils/toHierarchy";
+import { toHierarchy } from "carbon-components-svelte";
 
 describe("toHierarchy", () => {
   test("should create a flat hierarchy when no items have parents", () => {
@@ -102,4 +102,154 @@ describe("toHierarchy", () => {
 
     expect(result[0].nodes?.[0]).not.toHaveProperty("nodes");
   });
+
+  test("should handle empty input array", () => {
+    const result = toHierarchy<
+      { id: string | number; parentId?: string | number },
+      "parentId"
+    >([], (item) => item.parentId || null);
+    expect(result).toEqual([]);
+  });
+
+  test("should handle non-existent parent IDs", () => {
+    const input = [
+      { id: 1, name: "Root" },
+      { id: 2, name: "Child", pid: 999 },
+    ];
+    const result = toHierarchy(input, (item) => item.pid);
+    expect(result).toEqual([
+      { id: 1, name: "Root" },
+      { id: 2, name: "Child", pid: 999 },
+    ]);
+  });
+
+  test("should handle deeply nested structures", () => {
+    const input = [
+      { id: 1, name: "Level 1" },
+      { id: 2, name: "Level 2", pid: 1 },
+      { id: 3, name: "Level 3", pid: 2 },
+      { id: 4, name: "Level 4", pid: 3 },
+      { id: 5, name: "Level 5", pid: 4 },
+    ];
+    const result = toHierarchy(input, (item) => item.pid);
+    expect(result).toEqual([
+      {
+        id: 1,
+        name: "Level 1",
+        nodes: [
+          {
+            id: 2,
+            name: "Level 2",
+            pid: 1,
+            nodes: [
+              {
+                id: 3,
+                name: "Level 3",
+                pid: 2,
+                nodes: [
+                  {
+                    id: 4,
+                    name: "Level 4",
+                    pid: 3,
+                    nodes: [
+                      {
+                        id: 5,
+                        name: "Level 5",
+                        pid: 4,
+                      },
+                    ],
+                  },
+                ],
+              },
+            ],
+          },
+        ],
+      },
+    ]);
+  });
+
+  test("should handle mixed ID types", () => {
+    const input = [
+      { id: "root", name: "Root" },
+      { id: 1, name: "Child 1", pid: "root" },
+      { id: "2", name: "Child 2", pid: "root" },
+    ];
+    const result = toHierarchy(input, (item) => item.pid);
+    expect(result).toEqual([
+      {
+        id: "root",
+        name: "Root",
+        nodes: [
+          {
+            id: 1,
+            name: "Child 1",
+            pid: "root",
+          },
+          {
+            id: "2",
+            name: "Child 2",
+            pid: "root",
+          },
+        ],
+      },
+    ]);
+  });
+
+  test("should preserve additional properties", () => {
+    const input = [
+      { id: 1, name: "Root", extra: "data", meta: { key: "value" } },
+      { id: 2, name: "Child", pid: 1, flag: true, count: 42 },
+    ];
+    const result = toHierarchy(input, (item) => item.pid);
+    expect(result).toEqual([
+      {
+        id: 1,
+        name: "Root",
+        extra: "data",
+        meta: { key: "value" },
+        nodes: [
+          {
+            id: 2,
+            name: "Child",
+            pid: 1,
+            flag: true,
+            count: 42,
+          },
+        ],
+      },
+    ]);
+  });
+
+  test("should handle null/undefined parent IDs", () => {
+    const input = [
+      { id: 1, name: "Root 1" },
+      { id: 2, name: "Root 2", pid: null },
+      { id: 3, name: "Root 3", pid: undefined },
+      { id: 4, name: "Child", pid: 1 },
+    ];
+    const result = toHierarchy(input, (item) => item.pid);
+    expect(result).toEqual([
+      {
+        id: 1,
+        name: "Root 1",
+        nodes: [
+          {
+            id: 4,
+            name: "Child",
+            pid: 1,
+          },
+        ],
+      },
+      {
+        id: 2,
+        name: "Root 2",
+        pid: null,
+      },
+      {
+        id: 3,
+        name: "Root 3",
+        pid: undefined,
+      },
+    ]);
+  });
 });