diff --git a/packages/runtime-core/__tests__/debug.spec.ts b/packages/runtime-core/__tests__/debug.spec.ts
new file mode 100644
index 00000000000..f378b70c36d
--- /dev/null
+++ b/packages/runtime-core/__tests__/debug.spec.ts
@@ -0,0 +1,34 @@
+import {debug} from '../src/debug'
+import {
+  h,
+  render,
+  defineComponent,
+  ref, getCurrentInstance, ComponentInternalInstance, nodeOps,
+  serializeInner as inner
+} from '@vue/runtime-test'
+
+describe('debug', () => {
+  test('watching states', () => {
+    const root = nodeOps.createElement('div')
+    let instance: ComponentInternalInstance
+    const Comp = defineComponent({
+      setup() {
+        const name = ref('foo')
+        debug({
+          name,
+        })
+        return () => (
+          h('div', name.value)
+        )
+      },
+      mounted() {
+        instance = getCurrentInstance()!
+      },
+    })
+    render(h(Comp), root)
+    expect(inner(root)).toBe('<div>foo</div>')
+    expect(instance!.setupState).toEqual({
+      name: 'foo',
+    })
+  })
+})