Add first (failing) test for useState.

Author: ghengeveld

src/spec.js

@@ -1,7 +1,7 @@
 import "jest-dom/extend-expect"
 import React from "react"
 import { render, fireEvent, cleanup, waitForElement } from "react-testing-library"
-import Async, { createInstance } from "./"
+import Async, { createInstance, useAsync } from "./"
 
 afterEach(cleanup)
 
@@ -423,3 +423,10 @@ test("an unrelated change in props does not update the Context", async () => {
   )
   expect(one).toBe(two)
 })
+
+test("useAsync returns render props", async () => {
+  const promiseFn = () => new Promise(resolve => setTimeout(resolve, 0, "done"))
+  const Async = ({ children, ...props }) => children(useAsync(props))
+  const { getByText } = render(<Async promiseFn={promiseFn}>{({ data }) => data || null}</Async>)
+  await waitForElement(() => getByText("done"))
+})