diff --git a/src/keyHandler.ts b/src/keyHandler.ts
index 11feb139..8a686e12 100644
--- a/src/keyHandler.ts
+++ b/src/keyHandler.ts
@@ -7,8 +7,6 @@ import {
 } from "./jqtreeMethodTypes";
 import { Node } from "./node";
 
-type KeyboardEventHandler = (event: KeyboardEvent) => boolean;
-
 interface KeyHandlerParams {
     closeNode: CloseNode;
     getSelectedNode: GetSelectedNode;
@@ -55,7 +53,6 @@ export default class KeyHandler {
         }
     };
 
-    private handleKeyDownHandler?: KeyboardEventHandler;
     private isFocusOnTree: IsFocusOnTree;
     private keyboardSupport: boolean;
     private openNode: OpenNode;
@@ -127,8 +124,8 @@ export default class KeyHandler {
     }
 
     public deinit(): void {
-        if (this.handleKeyDownHandler) {
-            document.removeEventListener("keydown", this.handleKeyDownHandler);
+        if (this.keyboardSupport) {
+            document.removeEventListener("keydown", this.handleKeyDown);
         }
     }
 
diff --git a/src/nodeElement/folderElement.ts b/src/nodeElement/folderElement.ts
index 6e51596e..0ac2cc56 100644
--- a/src/nodeElement/folderElement.ts
+++ b/src/nodeElement/folderElement.ts
@@ -44,10 +44,7 @@ class FolderElement extends NodeElement {
         ) as HTMLLinkElement;
     }
 
-    public close(
-        slide = true,
-        animationSpeed: JQuery.Duration | undefined = "fast",
-    ): void {
+    public close(slide: boolean, animationSpeed: JQuery.Duration): void {
         if (!this.node.is_open) {
             return;
         }
@@ -86,8 +83,8 @@ class FolderElement extends NodeElement {
 
     public open(
         onFinished: OnFinishOpenNode | undefined,
-        slide = true,
-        animationSpeed: JQuery.Duration = "fast",
+        slide: boolean,
+        animationSpeed: JQuery.Duration,
     ): void {
         if (this.node.is_open) {
             return;
diff --git a/src/selectNodeHandler.ts b/src/selectNodeHandler.ts
index adbedc83..4510000d 100644
--- a/src/selectNodeHandler.ts
+++ b/src/selectNodeHandler.ts
@@ -64,18 +64,14 @@ export default class SelectNodeHandler {
                 return [];
             }
         } else {
-            const selectedNodes = [];
-
-            for (const id in this.selectedNodes) {
-                if (
-                    Object.prototype.hasOwnProperty.call(this.selectedNodes, id)
-                ) {
-                    const node = this.getNodeById(id);
-                    if (node && parent.isParentOf(node)) {
-                        selectedNodes.push(node);
-                    }
+            const selectedNodes: Node[] = [];
+
+            this.selectedNodes.forEach((id) => {
+                const node = this.getNodeById(id);
+                if (node && parent.isParentOf(node)) {
+                    selectedNodes.push(node);
                 }
-            }
+            });
 
             return selectedNodes;
         }
diff --git a/src/test/dataLoader.test.ts b/src/test/dataLoader.test.ts
new file mode 100644
index 00000000..7ade4a3f
--- /dev/null
+++ b/src/test/dataLoader.test.ts
@@ -0,0 +1,66 @@
+import { waitFor } from "@testing-library/dom";
+import { http, HttpResponse } from "msw";
+import { setupServer } from "msw/node";
+
+import DataLoader from "../dataLoader";
+
+const server = setupServer();
+
+afterAll(() => {
+    server.close();
+});
+
+afterEach(() => {
+    server.resetHandlers();
+});
+
+beforeAll(() => {
+    server.listen();
+});
+
+describe("loadFromUrl", () => {
+    it("does nothing when urlInfo is empty", () => {
+        const loadData = () => null;
+        const treeElement = document.createElement("div");
+        const triggerEvent = jest.fn();
+
+        const dataLoader = new DataLoader({
+            loadData,
+            treeElement,
+            triggerEvent,
+        });
+
+        dataLoader.loadFromUrl(null, null, null);
+        expect(triggerEvent).not.toHaveBeenCalled();
+    });
+
+    it("parses json when the response is a string", async () => {
+        server.use(
+            http.get(
+                "/test",
+                () =>
+                    new HttpResponse('{ "key1": "value1" }', {
+                        headers: {
+                            "Content-Type": "text/plain",
+                        },
+                    }),
+                {},
+            ),
+        );
+
+        const loadData = jest.fn();
+        const treeElement = document.createElement("div");
+        const triggerEvent = jest.fn();
+
+        const dataLoader = new DataLoader({
+            loadData,
+            treeElement,
+            triggerEvent,
+        });
+        dataLoader.loadFromUrl({ dataType: "text", url: "/test" }, null, null);
+
+        await waitFor(() => {
+            expect(loadData).toHaveBeenCalledWith({ key1: "value1" }, null);
+        });
+    });
+});
diff --git a/src/test/dragAndDropHandler/dragElement.test.ts b/src/test/dragAndDropHandler/dragElement.test.ts
new file mode 100644
index 00000000..0dcfb4b2
--- /dev/null
+++ b/src/test/dragAndDropHandler/dragElement.test.ts
@@ -0,0 +1,37 @@
+import DragElement from "../../dragAndDropHandler/dragElement";
+
+it("creates an element with autoEscape is true", () => {
+    const treeElement = document.createElement("div");
+
+    new DragElement({
+        autoEscape: true,
+        nodeName: "abc & def",
+        offsetX: 0,
+        offsetY: 0,
+        treeElement,
+    });
+
+    expect(treeElement.children.length).toBe(1);
+
+    const childElement = treeElement.children[0];
+    expect(childElement).toHaveClass("jqtree-title");
+    expect(childElement).toHaveClass("jqtree-dragging");
+    expect(childElement).toHaveTextContent("abc & def");
+});
+
+it("creates an element with autoEscape is false", () => {
+    const treeElement = document.createElement("div");
+
+    new DragElement({
+        autoEscape: false,
+        nodeName: "abc & def",
+        offsetX: 0,
+        offsetY: 0,
+        treeElement,
+    });
+
+    expect(treeElement.children.length).toBe(1);
+
+    const childElement = treeElement.children[0];
+    expect(childElement).toHaveTextContent("abc & def");
+});
diff --git a/src/test/jqTree/methods.test.ts b/src/test/jqTree/methods.test.ts
index cd26b662..f68846e4 100644
--- a/src/test/jqTree/methods.test.ts
+++ b/src/test/jqTree/methods.test.ts
@@ -300,6 +300,20 @@ describe("closeNode", () => {
     });
 });
 
+describe("destroy", () => {
+    it("clears the tree element", () => {
+        const $tree = $("#tree1");
+
+        $tree.tree({
+            data: exampleData,
+        });
+
+        $tree.tree("destroy");
+
+        expect($tree.get(0)).toBeEmptyDOMElement();
+    });
+});
+
 describe("getNodeByCallback", () => {
     interface Vars {
         $tree: JQuery;
diff --git a/src/test/selectNodeHandler.test.ts b/src/test/selectNodeHandler.test.ts
new file mode 100644
index 00000000..843b7d7c
--- /dev/null
+++ b/src/test/selectNodeHandler.test.ts
@@ -0,0 +1,24 @@
+import { Node } from "../node";
+import SelectNodeHandler from "../selectNodeHandler";
+
+describe("getSelectedNodesUnder", () => {
+    it("returns the nodes when the nodes have an id", () => {
+        const node = new Node({ id: 1 });
+
+        const child = new Node({ id: 2 });
+        node.addChild(child);
+
+        const nodeMap = new Map<NodeId, Node>();
+        nodeMap.set(1, node);
+        nodeMap.set(2, child);
+
+        const getNodeById = (id: NodeId) => nodeMap.get(id) ?? null;
+
+        const selectNodeHandler = new SelectNodeHandler({ getNodeById });
+        selectNodeHandler.addToSelection(child);
+
+        expect(
+            selectNodeHandler.getSelectedNodesUnder(node),
+        ).toIncludeAllMembers([child]);
+    });
+});