added result.error and change result.current into a getter that can throw if value is not valid

Author: mpeyper

README.md

@@ -138,6 +138,7 @@ Renders a test component that will call the provided `callback`, including any h
 
 - `result` (`object`)
   - `current` (`any`) - the return value of the `callback` function
+  - `error` (`Error`) - the error that was thrown if the `callback` function threw an error during rendering
 - `waitForNextUpdate` (`function`) - returns a `Promise` that resolves the next time the hook renders, commonly when state is updated as the result of a asynchronous action.
 - `rerender` (`function([newProps])`) - function to rerender the test component including any hooks called in the `callback` function. If `newProps` are passed, the will replace the `initialProps` passed the the `callback` function for future renders.
 - `unmount` (`function()`) - function to unmount the test component, commonly used to trigger cleanup effects for `useEffect` hooks.

src/index.js

@@ -2,38 +2,64 @@ import React from 'react'
 import { render, cleanup, act } from 'react-testing-library'
 
 function TestHook({ callback, hookProps, children }) {
-  children(callback(hookProps))
+  try {
+    children(callback(hookProps))
+  } catch (e) {
+    children(undefined, e)
+  }
   return null
 }
 
+function resultContainer() {
+  let value = null
+  let error = null
+  const resolvers = []
+
+  const result = {
+    get current() {
+      if (error) {
+        throw error
+      }
+      return value
+    },
+    get error() {
+      return error
+    }
+  }
+
+  return {
+    result,
+    addResolver: (resolver) => {
+      resolvers.push(resolver)
+    },
+    updateResult: (val, err) => {
+      value = val
+      error = err
+      resolvers.splice(0, resolvers.length).forEach((resolve) => resolve())
+    }
+  }
+}
+
 function renderHook(callback, { initialProps, ...options } = {}) {
-  const result = { current: null }
+  const { result, updateResult, addResolver } = resultContainer()
   const hookProps = { current: initialProps }
-  const resolvers = []
-  const waitForNextUpdate = () =>
-    new Promise((resolve) => {
-      resolvers.push(resolve)
-    })
 
   const toRender = () => (
     <TestHook callback={callback} hookProps={hookProps.current}>
-      {(res) => {
-        result.current = res
-        resolvers.splice(0, resolvers.length).forEach((resolve) => resolve())
-      }}
+      {updateResult}
     </TestHook>
   )
 
   const { unmount, rerender: rerenderComponent } = render(toRender(), options)
 
   return {
     result,
-    waitForNextUpdate,
-    unmount,
+    waitForNextUpdate: () => new Promise((resolve) => addResolver(resolve)),
     rerender: (newProps = hookProps.current) => {
       hookProps.current = newProps
       rerenderComponent(toRender())
-    }
+    },
+    unmount
   }
 }
 

test/errorHook.test.js

@@ -0,0 +1,108 @@
+import { useState, useEffect } from 'react'
+import { renderHook } from 'src'
+
+describe('error hook tests', () => {
+  function useError(throwError) {
+    if (throwError) {
+      throw new Error('expected')
+    }
+    return true
+  }
+
+  const somePromise = () => Promise.resolve()
+
+  function useAsyncError(throwError) {
+    const [value, setValue] = useState()
+    useEffect(() => {
+      somePromise().then(() => {
+        setValue(throwError)
+      })
+    }, [throwError])
+    return useError(value)
+  }
+
+  describe('synchronous', () => {
+    test('should raise error', () => {
+      const { result } = renderHook(() => useError(true))
+
+      expect(() => {
+        expect(result.current).not.toBe(undefined)
+      }).toThrow(Error('expected'))
+    })
+
+    test('should capture error', () => {
+      const { result } = renderHook(() => useError(true))
+
+      expect(result.error).toEqual(Error('expected'))
+    })
+
+    test('should not capture error', () => {
+      const { result } = renderHook(() => useError(false))
+
+      expect(result.current).not.toBe(undefined)
+      expect(result.error).toBe(undefined)
+    })
+
+    test('should reset error', () => {
+      const { result, rerender } = renderHook((throwError) => useError(throwError), {
+        initialProps: true
+      })
+
+      expect(result.error).not.toBe(undefined)
+
+      rerender(false)
+
+      expect(result.current).not.toBe(undefined)
+      expect(result.error).toBe(undefined)
+    })
+  })
+
+  describe('asynchronous', () => {
+    test('should raise async error', async () => {
+      const { result, waitForNextUpdate } = renderHook(() => useAsyncError(true))
+
+      await waitForNextUpdate()
+
+      expect(() => {
+        expect(result.current).not.toBe(undefined)
+      }).toThrow(Error('expected'))
+    })
+
+    test('should capture async error', async () => {
+      const { result, waitForNextUpdate } = renderHook(() => useAsyncError(true))
+
+      await waitForNextUpdate()
+
+      expect(result.error).toEqual(Error('expected'))
+    })
+
+    test('should not capture async error', async () => {
+      const { result, waitForNextUpdate } = renderHook(() => useAsyncError(false))
+
+      await waitForNextUpdate()
+
+      expect(result.current).not.toBe(undefined)
+      expect(result.error).toBe(undefined)
+    })
+
+    test('should reset async error', async () => {
+      const { result, waitForNextUpdate, rerender } = renderHook(
+        (throwError) => useAsyncError(throwError),
+        {
+          initialProps: true
+        }
+      )
+
+      await waitForNextUpdate()
+
+      expect(result.error).not.toBe(undefined)
+
+      rerender(false)
+
+      await waitForNextUpdate()
+
+      expect(result.current).not.toBe(undefined)
+      expect(result.error).toBe(undefined)
+    })
+  })
+})

test/typescript/renderHook.ts

@@ -65,6 +65,15 @@ function checkTypesWhenHookReturnsVoid() {
   const _rerender: () => void = rerender
 }
 
+function checkTypesWithError() {
+  const { result } = renderHook(() => useCounter())
+
+  // check types
+  const _result: {
+    error: Error
+  } = result
+}
+
 async function checkTypesForWaitForNextUpdate() {
   const { waitForNextUpdate } = renderHook(() => {})
 

typings/index.d.ts

@@ -7,7 +7,8 @@ export function renderHook<P, R>(
   } & RenderOptions
 ): {
   readonly result: {
-    current: R
+    readonly current: R,
+    readonly error: Error
   }
   readonly waitForNextUpdate: () => Promise<void>
   readonly unmount: RenderResult['unmount']