test: add test case for Q21 (webfansplz#545)

Author: holazz

questions/21-functional-component/README.md

@@ -0,0 +1,22 @@
+import { mount } from "@vue/test-utils"
+import { describe, it, expect } from "vitest"
+
+import App from "./App.vue"
+
+describe("functional-component", () => {
+  it("should work", async() => {
+    const wrapper = mount(App)
+    const list = wrapper.findComponent({ name: "list-component" })
+    expect(list.vm).toBeUndefined()
+
+    const item1 = list.findAll("li")[0]
+    const item2 = list.findAll("li")[1]
+    expect(item1.attributes("style")).toBe("color: red;")
+    expect(item2.attributes("style")).toBeUndefined()
+
+    await item2.trigger("click")
+
+    expect(item1.attributes("style")).toBeUndefined()
+    expect(item2.attributes("style")).toBe("color: red;")
+  })
+})