feat: Add renderHook

Author: eps1lon

src/__tests__/renderHook.js

@@ -0,0 +1,62 @@
+import React from 'react'
+import {renderHook} from '../pure'
+
+test('gives comitted result', () => {
+  const {result} = renderHook(() => {
+    const [state, setState] = React.useState(1)
+
+    React.useEffect(() => {
+      setState(2)
+    }, [])
+
+    return [state, setState]
+  })
+
+  expect(result.current).toEqual([2, expect.any(Function)])
+})
+
+test('allows rerendering', () => {
+  const {result, rerender} = renderHook(
+    ({branch}) => {
+      const [left, setLeft] = React.useState('left')
+      const [right, setRight] = React.useState('right')
+
+      // eslint-disable-next-line jest/no-if
+      switch (branch) {
+        case 'left':
+          return [left, setLeft]
+        case 'right':
+          return [right, setRight]
+
+        default:
+          throw new Error(
+            'No Props passed. This is a bug in the implementation',
+          )
+      }
+    },
+    {initialProps: {branch: 'left'}},
+  )
+
+  expect(result.current).toEqual(['left', expect.any(Function)])
+
+  rerender({branch: 'right'})
+
+  expect(result.current).toEqual(['right', expect.any(Function)])
+})
+
+test('allows wrapper components', async () => {
+  const Context = React.createContext('default')
+  function Wrapper({children}) {
+    return <Context.Provider value="provided">{children}</Context.Provider>
+  }
+  const {result} = renderHook(
+    () => {
+      return React.useContext(Context)
+    },
+    {
+      wrapper: Wrapper,
+    },
+  )
+
+  expect(result.current).toEqual('provided')
+})

src/pure.js

@@ -232,9 +232,37 @@ function cleanup() {
   mountedContainers.clear()
 }
 
+function renderHook(renderCallback, options = {}) {
+  const {initialProps, wrapper} = options
+  const result = React.createRef()
+
+  function TestComponent({renderCallbackProps}) {
+    const renderResult = renderCallback(renderCallbackProps)
+
+    React.useEffect(() => {
+      result.current = renderResult
+    })
+
+    return null
+  }
+
+  const {rerender: baseRerender, unmount} = render(
+    <TestComponent renderCallbackProps={initialProps} />,
+    {wrapper},
+  )
+
+  function rerender(rerenderCallbackProps) {
+    return baseRerender(
+      <TestComponent renderCallbackProps={rerenderCallbackProps} />,
+    )
+  }
+
+  return {result, rerender, unmount}
+}
+
 // just re-export everything from dom-testing-library
 export * from '@testing-library/dom'
-export {render, cleanup, act, fireEvent}
+export {render, renderHook, cleanup, act, fireEvent}
 
 // NOTE: we're not going to export asyncAct because that's our own compatibility
 // thing for people using [email protected]. Anyone else doesn't need it and