diff --git a/docs/unittest/ajax-simple-sub.json b/docs/unittest/ajax-simple-sub.json
new file mode 100644
index 0000000..1cef475
--- /dev/null
+++ b/docs/unittest/ajax-simple-sub.json
@@ -0,0 +1 @@
+[{ "title": "SubNode 1" }, { "title": "SubNode 2" }]
diff --git a/docs/unittest/ajax-simple.json b/docs/unittest/ajax-simple.json
new file mode 100644
index 0000000..76f8934
--- /dev/null
+++ b/docs/unittest/ajax-simple.json
@@ -0,0 +1,8 @@
+[
+  {
+    "title": "Node 1",
+    "expanded": true,
+    "children": [{ "title": "Node 1.1" }, { "title": "Node 1.2" }]
+  },
+  { "title": "Node 2", "lazy": true }
+]
diff --git a/docs/unittest/test-core-fixture1.js b/docs/unittest/test-core-fixture1.js
new file mode 100644
index 0000000..1c14dba
--- /dev/null
+++ b/docs/unittest/test-core-fixture1.js
@@ -0,0 +1,37 @@
+/*!
+ * Wunderbaum - Unit Test
+ * Copyright (c) 2021-2025, Martin Wendt. Released under the MIT license.
+ * @VERSION, @DATE (https://github.com/mar10/wunderbaum)
+ */
+
+const { test } = QUnit;
+const Wunderbaum = mar10.Wunderbaum;
+
+const FIXTURE_1 = [
+  {
+    title: "Node 1",
+    expanded: true,
+    children: [{ title: "Node 1.1" }, { title: "Node 1.2" }],
+  },
+  { title: "Node 2", lazy: true },
+];
+
+QUnit.module("Fixture-1 tests", (hooks) => {
+  let tree;
+
+  hooks.beforeEach(() => {
+    tree = new Wunderbaum({
+      element: "#tree",
+      source: FIXTURE_1,
+    });
+  });
+  hooks.afterEach(() => {
+    tree.destroy();
+    tree = null;
+  });
+
+  test("fixture ok", (assert) => {
+    assert.expect(1);
+    assert.equal(tree.count(), 4);
+  });
+});
diff --git a/docs/unittest/test-core.js b/docs/unittest/test-core.js
new file mode 100644
index 0000000..cf8b6fe
--- /dev/null
+++ b/docs/unittest/test-core.js
@@ -0,0 +1,225 @@
+/*!
+ * Wunderbaum - Unit Test
+ * Copyright (c) 2021-2025, Martin Wendt. Released under the MIT license.
+ * @VERSION, @DATE (https://github.com/mar10/wunderbaum)
+ */
+/* global mar10, QUnit */
+/* eslint-env browser */
+/* eslint-disable no-console */
+
+const { test } = QUnit;
+const Wunderbaum = mar10.Wunderbaum;
+const util = Wunderbaum.util;
+const FIXTURE_1 = [
+  {
+    title: "Node 1",
+    expanded: true,
+    children: [{ title: "Node 1.1" }, { title: "Node 1.2" }],
+  },
+  { title: "Node 2", lazy: true },
+];
+
+/* Setup */
+QUnit.testStart(function () {
+  window.sessionStorage.clear();
+  window.localStorage.clear();
+});
+
+/* Tear Down */
+QUnit.testDone(function () {});
+
+QUnit.module("Utility tests", (hooks) => {
+  test("Static utility functions", (assert) => {
+    assert.expect(2);
+
+    assert.equal(util.type([]), "array", "type([])");
+    assert.equal(util.type({}), "object", "type({})");
+  });
+});
+
+QUnit.module("Static tests", (hooks) => {
+  test("Access static properties", (assert) => {
+    assert.expect(4);
+
+    assert.true(Wunderbaum.version != null, "Statics defined");
+
+    assert.throws(
+      function () {
+        const _dummy = Wunderbaum();
+      },
+      /TypeError/,
+      "Fail if 'new' keyword is missing"
+    );
+    assert.throws(
+      function () {
+        const _dummy = new Wunderbaum();
+      },
+      /Error: Invalid 'element' option: null/,
+      "Fail if option is missing"
+    );
+    assert.throws(
+      function () {
+        const _dummy = new Wunderbaum({});
+      },
+      /Error: Invalid 'element' option: null/,
+      "Fail if 'element' option is missing"
+    );
+  });
+});
+
+QUnit.module("Instance tests", (hooks) => {
+  let tree = null;
+
+  hooks.beforeEach(() => {});
+  hooks.afterEach(() => {
+    tree.destroy();
+    tree = null;
+  });
+
+  test("Initial event sequence (fetch)", (assert) => {
+    assert.expect(5);
+    assert.timeout(1000); // Timeout after 1 second
+    const done = assert.async();
+
+    tree = new Wunderbaum({
+      element: "#tree",
+      source: "ajax-simple.json",
+      // source: FIXTURE_1,
+      receive: (e) => {
+        assert.step("receive");
+        assert.equal(
+          e.response[0].title,
+          "Node 1",
+          "receive(e) passes e.response"
+        );
+      },
+      load: (e) => {
+        assert.step("load");
+      },
+      // render: (e) => {
+      //   assert.step("render");
+      // },
+      init: (e) => {
+        assert.step("init");
+        assert.verifySteps(["receive", "load", "init"], "Event sequence");
+        done();
+      },
+    });
+  });
+
+  test("Lazy load (fetch)", (assert) => {
+    assert.expect(8);
+    assert.timeout(1000); // Timeout after 1 second
+    const done = assert.async();
+    let initComplete = false;
+
+    tree = new Wunderbaum({
+      element: "#tree",
+      source: "ajax-simple.json",
+      lazyLoad: (e) => {
+        if (initComplete) {
+          assert.step("lazyLoad");
+          assert.equal(
+            e.node.title,
+            "Node 2",
+            "lazyLoad(e) passes parent node"
+          );
+          return { url: "ajax-simple-sub.json" };
+        }
+      },
+      receive: (e) => {
+        if (initComplete) {
+          assert.step("receive");
+          assert.equal(
+            e.response[0].title,
+            "SubNode 1",
+            "receive(e) passes e.response"
+          );
+        }
+      },
+      load: (e) => {
+        if (initComplete) {
+          assert.step("load");
+          assert.verifySteps(
+            ["init", "lazyLoad", "receive", "load"],
+            "Event sequence"
+          );
+          done();
+        }
+      },
+      // render: (e) => {
+      //   assert.step("render");
+      // },
+      init: (e) => {
+        initComplete = true;
+        assert.step("init");
+        const lazyNode = tree.findFirst("Node 2");
+        assert.equal(lazyNode.title, "Node 2", "Find node by name");
+
+        // We need the markup, to issue a click event
+        // tree.updateViewport(true);
+        // assert.true(lazyNode.isRendered(), "Node is rendered");
+        // lazyNode.colspan.click();
+        lazyNode.setExpanded();
+      },
+    });
+  });
+
+  test("applyCommand", (assert) => {
+    assert.expect(2);
+    assert.timeout(1000); // Timeout after 1 second
+    const done = assert.async();
+
+    tree = new Wunderbaum({
+      element: "#tree",
+      source: FIXTURE_1,
+      init: (e) => {
+        const node1 = tree.findFirst("Node 1");
+        const node2 = tree.findFirst("Node 2");
+        assert.equal(node1.getPrevSibling(), null);
+
+        node1.applyCommand("moveDown");
+        assert.equal(node1.getPrevSibling(), node2);
+        // Avoid errors reported by ResizeObserver
+        done();
+      },
+    });
+  });
+  test("clones", (assert) => {
+    assert.expect(11);
+    assert.timeout(1000); // Timeout after 1 second
+    const done = assert.async();
+
+    tree = new Wunderbaum({
+      element: "#tree",
+      source: [
+        { title: "Node 1", key: "1", refKey: "n1" },
+        { title: "Node 2", key: "2", refKey: "nX" },
+        { title: "Node 3", key: "3", refKey: "nX" },
+      ],
+      init: (e) => {
+        const n1 = tree.findKey("1");
+        const n2 = tree.findKey("2");
+        const n3 = tree.findKey("3");
+
+        // console.warn(`tree.findByRefKey('nX'): >${tree.findByRefKey("nX")}<`);
+
+        assert.deepEqual(tree.findByRefKey("x"), []);
+        assert.deepEqual(tree.findByRefKey("n1"), [n1]);
+        assert.equal(tree.findByRefKey("nX").length, 2);
+
+        assert.false(n1.isClone());
+        assert.true(n2.isClone());
+        assert.true(n3.isClone());
+
+        assert.deepEqual(n1.getCloneList(), []);
+        assert.deepEqual(n1.getCloneList(true), [n1]);
+        assert.equal(n2.getCloneList().length, 1);
+        assert.equal(n2.getCloneList(false).length, 1);
+        assert.equal(n2.getCloneList(true).length, 2);
+
+        done();
+      },
+    });
+  });
+});
diff --git a/docs/unittest/test-dev.html b/docs/unittest/test-dev.html
new file mode 100644
index 0000000..179f4ef
--- /dev/null
+++ b/docs/unittest/test-dev.html
@@ -0,0 +1,28 @@
+<!DOCTYPE html>
+<html>
+<head>
+  <meta charset="utf-8">
+  <title>Test Suite (DEV) | Wunderbaum</title>
+
+  <!-- <link rel="stylesheet" href="https://code.jquery.com/qunit/qunit-2.15.0.css"> -->
+  <!-- <link rel="stylesheet" href="qunit.css"> -->
+  <link rel="stylesheet" href="../../node_modules/qunit/qunit/qunit.css">
+  <link rel="stylesheet" href="../../build/wunderbaum.css">
+
+  <!-- <script defer src="https://code.jquery.com/qunit/qunit-2.15.0.js"></script> -->
+  <!-- <script defer src="qunit.js"> </script> -->
+	<script src="../../node_modules/qunit/qunit/qunit.js"></script>
+
+  <script defer src="../../build/wunderbaum.umd.js"> </script>
+
+  <script defer type="module" src="test-core.js"> </script>
+  <script defer type="module" src="test-core-fixture1.js"> </script>
+</head>
+<body>
+  <div id="qunit"></div>
+  <div id="qunit-fixture"></div>
+
+  <div id="tree">
+  </div>
+</body>
+</html>
diff --git a/docs/unittest/test-dist.html b/docs/unittest/test-dist.html
new file mode 100644
index 0000000..943173e
--- /dev/null
+++ b/docs/unittest/test-dist.html
@@ -0,0 +1,23 @@
+<!DOCTYPE html>
+<html>
+<head>
+  <meta charset="utf-8">
+  <title>Test Suite (DIST) | Wunderbaum</title>
+
+  <link rel="stylesheet" href="https://code.jquery.com/qunit/qunit-2.18.1.css">
+  <link rel="stylesheet" href="https://cdn.jsdelivr.net/gh/mar10/wunderbaum/dist/wunderbaum.css">
+
+  <script defer src="https://code.jquery.com/qunit/qunit-2.18.1.js"></script>
+  <script defer src="https://cdn.jsdelivr.net/gh/mar10/wunderbaum/dist/wunderbaum.umd.min.js"> </script>
+
+  <script defer type="module" src="test-core.js"> </script>
+  <script defer type="module" src="test-core-fixture1.js"> </script>
+</head>
+<body>
+  <div id="qunit"></div>
+  <div id="qunit-fixture"></div>
+
+  <div id="tree">
+  </div>
+</body>
+</html>
diff --git a/unittest/ajax-simple-sub.json b/unittest/ajax-simple-sub.json
new file mode 100644
index 0000000..1cef475
--- /dev/null
+++ b/unittest/ajax-simple-sub.json
@@ -0,0 +1 @@
+[{ "title": "SubNode 1" }, { "title": "SubNode 2" }]
diff --git a/unittest/ajax-simple.json b/unittest/ajax-simple.json
new file mode 100644
index 0000000..76f8934
--- /dev/null
+++ b/unittest/ajax-simple.json
@@ -0,0 +1,8 @@
+[
+  {
+    "title": "Node 1",
+    "expanded": true,
+    "children": [{ "title": "Node 1.1" }, { "title": "Node 1.2" }]
+  },
+  { "title": "Node 2", "lazy": true }
+]
diff --git a/unittest/test-core-fixture1.js b/unittest/test-core-fixture1.js
new file mode 100644
index 0000000..1c14dba
--- /dev/null
+++ b/unittest/test-core-fixture1.js
@@ -0,0 +1,37 @@
+/*!
+ * Wunderbaum - Unit Test
+ * Copyright (c) 2021-2025, Martin Wendt. Released under the MIT license.
+ * @VERSION, @DATE (https://github.com/mar10/wunderbaum)
+ */
+
+const { test } = QUnit;
+const Wunderbaum = mar10.Wunderbaum;
+
+const FIXTURE_1 = [
+  {
+    title: "Node 1",
+    expanded: true,
+    children: [{ title: "Node 1.1" }, { title: "Node 1.2" }],
+  },
+  { title: "Node 2", lazy: true },
+];
+
+QUnit.module("Fixture-1 tests", (hooks) => {
+  let tree;
+
+  hooks.beforeEach(() => {
+    tree = new Wunderbaum({
+      element: "#tree",
+      source: FIXTURE_1,
+    });
+  });
+  hooks.afterEach(() => {
+    tree.destroy();
+    tree = null;
+  });
+
+  test("fixture ok", (assert) => {
+    assert.expect(1);
+    assert.equal(tree.count(), 4);
+  });
+});
diff --git a/unittest/test-core.js b/unittest/test-core.js
new file mode 100644
index 0000000..cf8b6fe
--- /dev/null
+++ b/unittest/test-core.js
@@ -0,0 +1,225 @@
+/*!
+ * Wunderbaum - Unit Test
+ * Copyright (c) 2021-2025, Martin Wendt. Released under the MIT license.
+ * @VERSION, @DATE (https://github.com/mar10/wunderbaum)
+ */
+/* global mar10, QUnit */
+/* eslint-env browser */
+/* eslint-disable no-console */
+
+const { test } = QUnit;
+const Wunderbaum = mar10.Wunderbaum;
+const util = Wunderbaum.util;
+const FIXTURE_1 = [
+  {
+    title: "Node 1",
+    expanded: true,
+    children: [{ title: "Node 1.1" }, { title: "Node 1.2" }],
+  },
+  { title: "Node 2", lazy: true },
+];
+
+/* Setup */
+QUnit.testStart(function () {
+  window.sessionStorage.clear();
+  window.localStorage.clear();
+});
+
+/* Tear Down */
+QUnit.testDone(function () {});
+
+QUnit.module("Utility tests", (hooks) => {
+  test("Static utility functions", (assert) => {
+    assert.expect(2);
+
+    assert.equal(util.type([]), "array", "type([])");
+    assert.equal(util.type({}), "object", "type({})");
+  });
+});
+
+QUnit.module("Static tests", (hooks) => {
+  test("Access static properties", (assert) => {
+    assert.expect(4);
+
+    assert.true(Wunderbaum.version != null, "Statics defined");
+
+    assert.throws(
+      function () {
+        const _dummy = Wunderbaum();
+      },
+      /TypeError/,
+      "Fail if 'new' keyword is missing"
+    );
+    assert.throws(
+      function () {
+        const _dummy = new Wunderbaum();
+      },
+      /Error: Invalid 'element' option: null/,
+      "Fail if option is missing"
+    );
+    assert.throws(
+      function () {
+        const _dummy = new Wunderbaum({});
+      },
+      /Error: Invalid 'element' option: null/,
+      "Fail if 'element' option is missing"
+    );
+  });
+});
+
+QUnit.module("Instance tests", (hooks) => {
+  let tree = null;
+
+  hooks.beforeEach(() => {});
+  hooks.afterEach(() => {
+    tree.destroy();
+    tree = null;
+  });
+
+  test("Initial event sequence (fetch)", (assert) => {
+    assert.expect(5);
+    assert.timeout(1000); // Timeout after 1 second
+    const done = assert.async();
+
+    tree = new Wunderbaum({
+      element: "#tree",
+      source: "ajax-simple.json",
+      // source: FIXTURE_1,
+      receive: (e) => {
+        assert.step("receive");
+        assert.equal(
+          e.response[0].title,
+          "Node 1",
+          "receive(e) passes e.response"
+        );
+      },
+      load: (e) => {
+        assert.step("load");
+      },
+      // render: (e) => {
+      //   assert.step("render");
+      // },
+      init: (e) => {
+        assert.step("init");
+        assert.verifySteps(["receive", "load", "init"], "Event sequence");
+        done();
+      },
+    });
+  });
+
+  test("Lazy load (fetch)", (assert) => {
+    assert.expect(8);
+    assert.timeout(1000); // Timeout after 1 second
+    const done = assert.async();
+    let initComplete = false;
+
+    tree = new Wunderbaum({
+      element: "#tree",
+      source: "ajax-simple.json",
+      lazyLoad: (e) => {
+        if (initComplete) {
+          assert.step("lazyLoad");
+          assert.equal(
+            e.node.title,
+            "Node 2",
+            "lazyLoad(e) passes parent node"
+          );
+          return { url: "ajax-simple-sub.json" };
+        }
+      },
+      receive: (e) => {
+        if (initComplete) {
+          assert.step("receive");
+          assert.equal(
+            e.response[0].title,
+            "SubNode 1",
+            "receive(e) passes e.response"
+          );
+        }
+      },
+      load: (e) => {
+        if (initComplete) {
+          assert.step("load");
+          assert.verifySteps(
+            ["init", "lazyLoad", "receive", "load"],
+            "Event sequence"
+          );
+          done();
+        }
+      },
+      // render: (e) => {
+      //   assert.step("render");
+      // },
+      init: (e) => {
+        initComplete = true;
+        assert.step("init");
+        const lazyNode = tree.findFirst("Node 2");
+        assert.equal(lazyNode.title, "Node 2", "Find node by name");
+
+        // We need the markup, to issue a click event
+        // tree.updateViewport(true);
+        // assert.true(lazyNode.isRendered(), "Node is rendered");
+        // lazyNode.colspan.click();
+        lazyNode.setExpanded();
+      },
+    });
+  });
+
+  test("applyCommand", (assert) => {
+    assert.expect(2);
+    assert.timeout(1000); // Timeout after 1 second
+    const done = assert.async();
+
+    tree = new Wunderbaum({
+      element: "#tree",
+      source: FIXTURE_1,
+      init: (e) => {
+        const node1 = tree.findFirst("Node 1");
+        const node2 = tree.findFirst("Node 2");
+        assert.equal(node1.getPrevSibling(), null);
+
+        node1.applyCommand("moveDown");
+        assert.equal(node1.getPrevSibling(), node2);
+        // Avoid errors reported by ResizeObserver
+        done();
+      },
+    });
+  });
+  test("clones", (assert) => {
+    assert.expect(11);
+    assert.timeout(1000); // Timeout after 1 second
+    const done = assert.async();
+
+    tree = new Wunderbaum({
+      element: "#tree",
+      source: [
+        { title: "Node 1", key: "1", refKey: "n1" },
+        { title: "Node 2", key: "2", refKey: "nX" },
+        { title: "Node 3", key: "3", refKey: "nX" },
+      ],
+      init: (e) => {
+        const n1 = tree.findKey("1");
+        const n2 = tree.findKey("2");
+        const n3 = tree.findKey("3");
+
+        // console.warn(`tree.findByRefKey('nX'): >${tree.findByRefKey("nX")}<`);
+
+        assert.deepEqual(tree.findByRefKey("x"), []);
+        assert.deepEqual(tree.findByRefKey("n1"), [n1]);
+        assert.equal(tree.findByRefKey("nX").length, 2);
+
+        assert.false(n1.isClone());
+        assert.true(n2.isClone());
+        assert.true(n3.isClone());
+
+        assert.deepEqual(n1.getCloneList(), []);
+        assert.deepEqual(n1.getCloneList(true), [n1]);
+        assert.equal(n2.getCloneList().length, 1);
+        assert.equal(n2.getCloneList(false).length, 1);
+        assert.equal(n2.getCloneList(true).length, 2);
+
+        done();
+      },
+    });
+  });
+});
diff --git a/unittest/test-dev.html b/unittest/test-dev.html
new file mode 100644
index 0000000..179f4ef
--- /dev/null
+++ b/unittest/test-dev.html
@@ -0,0 +1,28 @@
+<!DOCTYPE html>
+<html>
+<head>
+  <meta charset="utf-8">
+  <title>Test Suite (DEV) | Wunderbaum</title>
+
+  <!-- <link rel="stylesheet" href="https://code.jquery.com/qunit/qunit-2.15.0.css"> -->
+  <!-- <link rel="stylesheet" href="qunit.css"> -->
+  <link rel="stylesheet" href="../../node_modules/qunit/qunit/qunit.css">
+  <link rel="stylesheet" href="../../build/wunderbaum.css">
+
+  <!-- <script defer src="https://code.jquery.com/qunit/qunit-2.15.0.js"></script> -->
+  <!-- <script defer src="qunit.js"> </script> -->
+	<script src="../../node_modules/qunit/qunit/qunit.js"></script>
+
+  <script defer src="../../build/wunderbaum.umd.js"> </script>
+
+  <script defer type="module" src="test-core.js"> </script>
+  <script defer type="module" src="test-core-fixture1.js"> </script>
+</head>
+<body>
+  <div id="qunit"></div>
+  <div id="qunit-fixture"></div>
+
+  <div id="tree">
+  </div>
+</body>
+</html>
diff --git a/unittest/test-dist.html b/unittest/test-dist.html
new file mode 100644
index 0000000..943173e
--- /dev/null
+++ b/unittest/test-dist.html
@@ -0,0 +1,23 @@
+<!DOCTYPE html>
+<html>
+<head>
+  <meta charset="utf-8">
+  <title>Test Suite (DIST) | Wunderbaum</title>
+
+  <link rel="stylesheet" href="https://code.jquery.com/qunit/qunit-2.18.1.css">
+  <link rel="stylesheet" href="https://cdn.jsdelivr.net/gh/mar10/wunderbaum/dist/wunderbaum.css">
+
+  <script defer src="https://code.jquery.com/qunit/qunit-2.18.1.js"></script>
+  <script defer src="https://cdn.jsdelivr.net/gh/mar10/wunderbaum/dist/wunderbaum.umd.min.js"> </script>
+
+  <script defer type="module" src="test-core.js"> </script>
+  <script defer type="module" src="test-core-fixture1.js"> </script>
+</head>
+<body>
+  <div id="qunit"></div>
+  <div id="qunit-fixture"></div>
+
+  <div id="tree">
+  </div>
+</body>
+</html>