More tetst added.

src/components/button/Button.test.tsx

@@ -1,6 +1,7 @@
 import React from 'react'
-import ReactDOM from 'react-dom';
-import Button from './Button';
+import ReactDOM from 'react-dom'
+import Button from './Button'
+import { render, fireEvent, waitForElement, waitForDomChange } from '@testing-library/react'
 
 describe('Button component', () => {
     it('renders without crashing', () => {
@@ -9,3 +10,16 @@ describe('Button component', () => {
         ReactDOM.unmountComponentAtNode(div);
     });
 })
+
+describe('Dom updates', () => {
+    it('should update button label to "Hello 2"', async (done) => {
+        const {getByTestId} = render(<Button interval={500}/>)
+        const el = await waitForElement(() => getByTestId('btn')) as HTMLButtonElement
+        fireEvent.click(el)
+        fireEvent.click(el)
+        fireEvent.click(el)
+        const t = await waitForDomChange({container: el})
+        expect(el.textContent).toEqual('Hello 2')
+        done()
+    })
+})

src/components/button/Button.tsx

@@ -1,12 +1,14 @@
 import React, { SFC} from 'react'
+import {useClick} from './useClick'
 
 type Props = {
     interval?: number;
     label?:string;
 }
 
 const Button:SFC<Props> = (props:Props) => {
-    return <button data-testid="btn">Hello</button>
+    const {ref, count} = useClick(props.interval)
+    return <button data-testid="btn" ref={ref}>Hello {count}</button>
 }
 
 export default Button