feat: add render hook

src/__tests__/renderHook.js

@@ -0,0 +1,62 @@
+import { createContext, h } from 'preact'
+import { useState, useContext, useEffect } from 'preact/hooks'
+import { renderHook } from '../pure'
+
+test('gives comitted result', () => {
+  const { result } = renderHook(() => {
+    const [state, setState] = useState(1)
+
+    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] = useState('left')
+      const [right, setRight] = useState('right')
+
+      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 = createContext('default')
+  function Wrapper ({ children }) {
+    return <Context.Provider value="provided">{children}</Context.Provider>
+  }
+  const { result } = renderHook(
+    () => {
+      return useContext(Context)
+    },
+    {
+      wrapper: Wrapper
+    }
+  )
+
+  expect(result.current).toEqual('provided')
+})

src/pure.js

@@ -1,5 +1,6 @@
 import { getQueriesForElement, prettyDOM, configure as configureDTL } from '@testing-library/dom'
-import { h, hydrate as preactHydrate, render as preactRender } from 'preact'
+import { h, hydrate as preactHydrate, render as preactRender, createRef } from 'preact'
+import { useEffect } from 'preact/hooks'
 import { act } from 'preact/test-utils'
 import { fireEvent } from './fire-event'
 
@@ -107,7 +108,35 @@ function cleanup () {
   mountedContainers.forEach(cleanupAtContainer)
 }
 
+function renderHook (renderCallback, options) {
+  const { initialProps, wrapper } = (options || {})
+  const result = createRef()
+
+  function TestComponent ({ renderCallbackProps }) {
+    const pendingResult = renderCallback(renderCallbackProps)
+
+    useEffect(() => {
+      result.current = pendingResult
+    })
+
+    return null
+  }
+
+  const { rerender: baseRerender, unmount } = render(
+    <TestComponent renderCallbackProps={initialProps} />,
+    { wrapper }
+  )
+
+  function rerender (rerenderCallbackProps) {
+    return baseRerender(
+      <TestComponent renderCallbackProps={rerenderCallbackProps} />
+    )
+  }
+
+  return { result, rerender, unmount }
+}
+
 // eslint-disable-next-line import/export
 export * from '@testing-library/dom'
 // eslint-disable-next-line import/export
-export { render, cleanup, act, fireEvent }
+export { render, cleanup, act, fireEvent, renderHook }

types/index.d.ts

@@ -1,6 +1,6 @@
 import { queries, Queries, BoundFunction } from '@testing-library/dom'
 import { act as preactAct } from 'preact/test-utils'
-import { ComponentChild } from 'preact'
+import { ComponentChild, ComponentType, Element } from 'preact'
 
 export * from '@testing-library/dom'
 
@@ -46,3 +46,49 @@ export function cleanup(): void
 export const act: typeof preactAct extends undefined
   ? (callback: () => void) => void
   : typeof preactAct
+
+export interface RenderHookResult<Result, Props> {
+  /**
+   * Triggers a re-render. The props will be passed to your renderHook callback.
+   */
+  rerender: (props?: Props) => void
+  /**
+   * This is a stable reference to the latest value returned by your renderHook
+   * callback
+   */
+  result: {
+    /**
+     * The value returned by your renderHook callback
+     */
+    current: Result
+  }
+  /**
+   * Unmounts the test component. This is useful for when you need to test
+   * any cleanup your useEffects have.
+   */
+  unmount: () => void
+}
+
+export interface RenderHookOptions<Props> {
+  /**
+   * The argument passed to the renderHook callback. Can be useful if you plan
+   * to use the rerender utility to change the values passed to your hook.
+   */
+  initialProps?: Props
+  /**
+   * Pass a React Component as the wrapper option to have it rendered around the inner element. This is most useful for creating
+   *  reusable custom render functions for common data providers. See setup for examples.
+   *
+   *  @see https://testing-library.com/docs/react-testing-library/api/#wrapper
+   */
+  wrapper?: ComponentType<{ children: Element }>
+}
+
+/**
+ * Allows you to render a hook within a test React component without having to
+ * create that component yourself.
+ */
+export function renderHook<Result, Props>(
+  render: (initialProps: Props) => Result,
+  options?: RenderHookOptions<Props>,
+): RenderHookResult<Result, Props>