feat: testHook returns result ref object (#297)

Author: FredyC

src/__tests__/test-hook.js

@@ -1,6 +1,6 @@
 import React, {useState, useEffect} from 'react'
 import 'jest-dom/extend-expect'
-import {testHook, cleanup} from '../'
+import {testHook, cleanup, act} from '../'
 
 afterEach(cleanup)
 
@@ -60,3 +60,18 @@ test('accepts wrapper option to wrap rendered hook with', () => {
   )
   expect(actual).toBe(12)
 })
+test('returns result ref with latest result from hook execution', () => {
+  function useCounter({initialCount = 0, step = 1} = {}) {
+    const [count, setCount] = React.useState(initialCount)
+    const increment = () => setCount(c => c + step)
+    const decrement = () => setCount(c => c - step)
+    return {count, increment, decrement}
+  }
+
+  const {result} = testHook(useCounter)
+  expect(result.current.count).toBe(0)
+  act(() => {
+    result.current.increment()
+  })
+  expect(result.current.count).toBe(1)
+})

src/index.js

@@ -61,21 +61,31 @@ function render(
   }
 }
 
-function TestHook({callback}) {
-  callback()
+function TestHook({callback, children}) {
+  children(callback())
   return null
 }
 
 function testHook(callback, options = {}) {
+  const result = {
+    current: null,
+  }
   const toRender = () => {
-    const hookRender = <TestHook callback={callback} />
+    const hookRender = (
+      <TestHook callback={callback}>
+        {res => {
+          result.current = res
+        }}
+      </TestHook>
+    )
     if (options.wrapper) {
       return React.createElement(options.wrapper, null, hookRender)
     }
     return hookRender
   }
   const {unmount, rerender: rerenderComponent} = render(toRender())
   return {
+    result,
     unmount,
     rerender: () => {
       rerenderComponent(toRender())

typings/index.d.ts

@@ -19,7 +19,8 @@ export type RenderResult<Q extends Queries = typeof queries> = {
   asFragment: () => DocumentFragment
 } & {[P in keyof Q]: BoundFunction<Q[P]>}
 
-export type HookResult = {
+export type HookResult<TResult> = {
+  result: React.MutableRefObject<TResult>
   rerender: () => void
   unmount: () => boolean
 }
@@ -52,7 +53,10 @@ export function render<Q extends Queries>(
 /**
  * Renders a test component that calls back to the test.
  */
-export function testHook(callback: () => void, options?: Partial<HookOptions>): HookResult
+export function testHook<T>(
+  callback: () => T,
+  options?: Partial<HookOptions>,
+): HookResult<T>
 
 /**
  * Unmounts React trees that were mounted with render.