diff --git a/tests/cypress/integration/core/extendExtensions.spec.ts b/tests/cypress/integration/core/extendExtensions.spec.ts
new file mode 100644
index 000000000..b172fe6e7
--- /dev/null
+++ b/tests/cypress/integration/core/extendExtensions.spec.ts
@@ -0,0 +1,134 @@
+/// <reference types="cypress" />
+
+import { Extension } from '@tiptap/core/src/Extension'
+import getExtensionField from '@tiptap/core/src/helpers/getExtensionField'
+
+describe('extend extensions', () => {
+  it('should define a config', () => {
+    const extension = Extension.create({
+      addAttributes() {
+        return {
+          foo: {},
+        }
+      },
+    })
+
+    const attributes = getExtensionField(extension, 'addAttributes')()
+
+    expect(attributes).to.deep.eq({
+      foo: {},
+    })
+  })
+
+  it('should overwrite a config', () => {
+    const extension = Extension
+      .create({
+        addAttributes() {
+          return {
+            foo: {},
+          }
+        },
+      })
+      .extend({
+        addAttributes() {
+          return {
+            bar: {},
+          }
+        },
+      })
+
+    const attributes = getExtensionField(extension, 'addAttributes')()
+
+    expect(attributes).to.deep.eq({
+      bar: {},
+    })
+  })
+
+  it('should merge configs', () => {
+    const extension = Extension
+      .create({
+        addAttributes() {
+          return {
+            foo: {},
+          }
+        },
+      })
+      .extend({
+        addAttributes() {
+          return {
+            ...this.parent?.(),
+            bar: {},
+          }
+        },
+      })
+
+    const attributes = getExtensionField(extension, 'addAttributes')()
+
+    expect(attributes).to.deep.eq({
+      foo: {},
+      bar: {},
+    })
+  })
+
+  it('should merge configs multiple times', () => {
+    const extension = Extension
+      .create({
+        addAttributes() {
+          return {
+            foo: {},
+          }
+        },
+      })
+      .extend({
+        addAttributes() {
+          return {
+            ...this.parent?.(),
+            bar: {},
+          }
+        },
+      })
+      .extend({
+        addAttributes() {
+          return {
+            ...this.parent?.(),
+            baz: {},
+          }
+        },
+      })
+
+    const attributes = getExtensionField(extension, 'addAttributes')()
+
+    expect(attributes).to.deep.eq({
+      foo: {},
+      bar: {},
+      baz: {},
+    })
+  })
+
+  it('should merge configs without direct parent configuration', () => {
+    const extension = Extension
+      .create({
+        addAttributes() {
+          return {
+            foo: {},
+          }
+        },
+      })
+      .extend()
+      .extend({
+        addAttributes() {
+          return {
+            ...this.parent?.(),
+            bar: {},
+          }
+        },
+      })
+
+    const attributes = getExtensionField(extension, 'addAttributes')()
+
+    expect(attributes).to.deep.eq({
+      foo: {},
+      bar: {},
+    })
+  })
+})