diff --git a/src/test/scrollHandler/documentScrollParent.test.ts b/src/test/scrollHandler/documentScrollParent.test.ts
new file mode 100644
index 00000000..42c82353
--- /dev/null
+++ b/src/test/scrollHandler/documentScrollParent.test.ts
@@ -0,0 +1,60 @@
+import DocumentScrollParent from "../../scrollHandler/documentScrollParent";
+
+afterEach(() => {
+    jest.useRealTimers();
+});
+
+describe("checkHorizontalScrolling", () => {
+    it("scrolls to the left when pageX is near the left edge", () => {
+        jest.useFakeTimers();
+        const scrollBy = jest.fn();
+        window.scrollBy = scrollBy;
+
+        const refreshHitAreas = jest.fn();
+        const treeElement = document.createElement("div");
+
+        const documentScrollParent = new DocumentScrollParent({
+            refreshHitAreas,
+            treeElement,
+        });
+
+        documentScrollParent.checkHorizontalScrolling(10);
+
+        expect(scrollBy).not.toHaveBeenCalled();
+        jest.advanceTimersByTime(50);
+        expect(scrollBy).toHaveBeenCalledWith({
+            behavior: "instant",
+            left: -20,
+            top: 0,
+        });
+    });
+
+    it("stops scrolling when pageX is moved from the left edge", () => {
+        jest.useFakeTimers();
+        const scrollBy = jest.fn();
+        window.scrollBy = scrollBy;
+
+        const refreshHitAreas = jest.fn();
+        const treeElement = document.createElement("div");
+
+        const documentScrollParent = new DocumentScrollParent({
+            refreshHitAreas,
+            treeElement,
+        });
+
+        documentScrollParent.checkHorizontalScrolling(10);
+
+        expect(scrollBy).not.toHaveBeenCalled();
+        jest.advanceTimersByTime(50);
+        expect(scrollBy).toHaveBeenCalledWith({
+            behavior: "instant",
+            left: -20,
+            top: 0,
+        });
+
+        documentScrollParent.checkHorizontalScrolling(100);
+        jest.advanceTimersByTime(50);
+
+        expect(scrollBy).toHaveBeenCalledTimes(1);
+    });
+});
diff --git a/src/test/support/testUtil.ts b/src/test/support/testUtil.ts
index 7d17d4ca..7410ecf7 100644
--- a/src/test/support/testUtil.ts
+++ b/src/test/support/testUtil.ts
@@ -34,7 +34,7 @@ export const togglerLink = (liNode: HTMLElement | JQuery): JQuery =>
 const nodeElement = (liNode: HTMLElement | JQuery): JQuery =>
     singleChild(jQuery(liNode), "div.jqtree-element ");
 
-export const mockLayout = (element: HTMLElement, rect: Rect) => {
+const mockLayout = (element: HTMLElement, rect: Rect) => {
     jest.spyOn(element, "clientHeight", "get").mockReturnValue(rect.height);
     jest.spyOn(element, "clientWidth", "get").mockReturnValue(rect.width);
     jest.spyOn(element, "offsetParent", "get").mockReturnValue(