diff --git a/.github/workflows/build.yml b/.github/workflows/build.yml
index 751a38c3b..07816276e 100644
--- a/.github/workflows/build.yml
+++ b/.github/workflows/build.yml
@@ -49,6 +49,9 @@ jobs:
       - name: Generate @maxgraph/core types
         working-directory: packages/core
         run: npm run generate-types
+      - name: Test @maxgraph/core
+        working-directory: packages/core
+        run: npm test
       - name: Test TypeScript support
         working-directory: packages/ts-support
         run: npm test
diff --git a/packages/core/__tests__/view/cell/CellOverlay.test.ts b/packages/core/__tests__/view/cell/CellOverlay.test.ts
new file mode 100644
index 000000000..2923d878d
--- /dev/null
+++ b/packages/core/__tests__/view/cell/CellOverlay.test.ts
@@ -0,0 +1,40 @@
+/*
+Copyright 2022-present The maxGraph project Contributors
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+import { describe, expect, test } from '@jest/globals';
+import { CellOverlay, Point } from '../../../src';
+
+test('Constructor set all parameters', () => {
+  const cellOverlay = new CellOverlay(
+    // @ts-ignore
+    null,
+    'my tooltip',
+    'left',
+    'middle',
+    new Point(10, 20),
+    'custom'
+  );
+
+  expect(cellOverlay).toEqual(
+    expect.objectContaining({
+      align: 'left',
+      cursor: 'custom',
+      offset: new Point(10, 20),
+      tooltip: 'my tooltip',
+      verticalAlign: 'middle',
+    })
+  );
+});
diff --git a/packages/core/jest.config.cjs b/packages/core/jest.config.cjs
new file mode 100644
index 000000000..95a72e799
--- /dev/null
+++ b/packages/core/jest.config.cjs
@@ -0,0 +1,6 @@
+/** @type {import('ts-jest').JestConfigWithTsJest} */
+module.exports = {
+  // preset: 'ts-jest',
+  preset: 'ts-jest/presets/default-esm',
+  testEnvironment: 'jsdom', // need to access to the browser objects
+};
diff --git a/packages/core/package.json b/packages/core/package.json
index ab7cf4134..9daed5cf7 100644
--- a/packages/core/package.json
+++ b/packages/core/package.json
@@ -22,11 +22,15 @@
     "build": "cross-env NODE_ENV=production webpack --mode=production",
     "generate-types": "tsc --emitDeclarationOnly",
     "generate-esm": "tsc --emitDeclarationOnly false --declaration false --declarationDir null",
-    "prepack": "run-s generate-types generate-esm build"
+    "prepack": "run-s generate-types generate-esm build",
+    "test": "jest"
   },
   "devDependencies": {
     "circular-dependency-plugin": "^5.2.2",
-    "npm-run-all": "~4.1.5"
+    "jest": "^29.3.1",
+    "jest-environment-jsdom": "^29.3.1",
+    "npm-run-all": "~4.1.5",
+    "ts-jest": "^29.0.3"
   },
   "sideEffects": true
 }
diff --git a/packages/core/src/view/cell/CellOverlay.ts b/packages/core/src/view/cell/CellOverlay.ts
index b14d9a6c3..fd09bb74e 100644
--- a/packages/core/src/view/cell/CellOverlay.ts
+++ b/packages/core/src/view/cell/CellOverlay.ts
@@ -22,6 +22,7 @@ import EventSource from '../event/EventSource';
 import ImageBox from '../image/ImageBox';
 import CellState from './CellState';
 import ObjectIdentity from '../../util/ObjectIdentity';
+import { AlignValue, VAlignValue } from '../../types';
 
 /**
  * Extends {@link EventSource} to implement a graph overlay, represented by an icon
@@ -77,8 +78,8 @@ class CellOverlay extends EventSource implements ObjectIdentity {
   constructor(
     image: ImageBox,
     tooltip: string | null = null,
-    align = 'right',
-    verticalAlign = 'bottom',
+    align: AlignValue = 'right',
+    verticalAlign: VAlignValue = 'bottom',
     offset: Point = new Point(),
     cursor = 'help'
   ) {
@@ -86,6 +87,8 @@ class CellOverlay extends EventSource implements ObjectIdentity {
 
     this.image = image;
     this.tooltip = tooltip;
+    this.align = align;
+    this.verticalAlign = verticalAlign;
     this.offset = offset;
     this.cursor = cursor;
   }
@@ -101,18 +104,20 @@ class CellOverlay extends EventSource implements ObjectIdentity {
   tooltip?: string | null;
 
   /**
-   * Holds the horizontal alignment for the overlay. Default is
-   * {@link Constants#ALIGN_RIGHT}. For edges, the overlay always appears in the
-   * center of the edge.
+   * Holds the horizontal alignment for the overlay.
+   *
+   * For edges, the overlay always appears in the center of the edge.
+   * @default 'right'
    */
-  align: 'left' | 'center' | 'right' = 'right';
+  align: AlignValue = 'right';
 
   /**
-   * Holds the vertical alignment for the overlay. Default is
-   * {@link Constants#ALIGN_BOTTOM}. For edges, the overlay always appears in the
-   * center of the edge.
+   * Holds the vertical alignment for the overlay.
+   *
+   * For edges, the overlay always appears in the center of the edge.
+   * @default 'bottom'
    */
-  verticalAlign: 'top' | 'middle' | 'bottom' = 'bottom';
+  verticalAlign: VAlignValue = 'bottom';
 
   /**
    * Holds the offset as an {@link Point}. The offset will be scaled according to the
@@ -121,7 +126,8 @@ class CellOverlay extends EventSource implements ObjectIdentity {
   offset = new Point();
 
   /**
-   * Holds the cursor for the overlay. Default is 'help'.
+   * Holds the cursor for the overlay.
+   * @default 'help'.
    */
   cursor = 'help';
 
diff --git a/packages/html/stories/Overlays.stories.js b/packages/html/stories/Overlays.stories.js
index db7ca7f89..df662b38e 100644
--- a/packages/html/stories/Overlays.stories.js
+++ b/packages/html/stories/Overlays.stories.js
@@ -54,6 +54,14 @@ const Template = ({ label, ...args }) => {
   // Enables tooltips for the overlays
   graph.setTooltips(true);
 
+  function pickAlignValueRandomly() {
+    return ['left', 'center', 'right'][Math.floor(Math.random() * 3)];
+  }
+
+  function pickVerticalAlignValueRandomly() {
+    return ['top', 'bottom'][Math.floor(Math.random() * 2)];
+  }
+
   // Installs a handler for click events in the graph
   // that toggles the overlay for the respective cell
   graph.addListener(InternalEvent.CLICK, (sender, evt) => {
@@ -61,12 +69,13 @@ const Template = ({ label, ...args }) => {
 
     if (cell != null) {
       const overlays = graph.getCellOverlays(cell);
-
-      if (overlays.length == 0) {
+      if (overlays.length === 0) {
         // Creates a new overlay with an image and a tooltip
         const overlay = new CellOverlay(
           new ImageBox('/images/check.png', 16, 16),
-          'Overlay tooltip'
+          'Overlay tooltip',
+          pickAlignValueRandomly(),
+          pickVerticalAlignValueRandomly()
         );
 
         // Installs a handler for clicks on the overlay
@@ -104,7 +113,7 @@ const Template = ({ label, ...args }) => {
     });
     const v2 = graph.insertVertex({
       parent,
-      value: 'Doubleclick',
+      value: 'Double Click',
       position: [200, 150],
       size: [100, 40],
     });