Capture all results a rendered hook produces. (#496)

feat: Capture all results a rendered hook produces as `result.all`

Fixes #461

Co-authored-by: Josh Ellis <[email protected]>

Author: mpeyper

Diff for: docs/api-reference.md

@@ -63,13 +63,17 @@ The `renderHook` function returns an object that has the following properties:
 
 ```js
 {
+  all: Array<any>
   current: any,
   error: Error
 }
 ```
 
-The `current` value or the `result` will reflect whatever is returned from the `callback` passed to
-`renderHook`. Any thrown values will be reflected in the `error` value of the `result`.
+The `current` value or the `result` will reflect the latest of whatever is returned from the
+`callback` passed to `renderHook`. Any thrown values from the latest call will be reflected in the
+`error` value of the `result`. The `all` value is an array containing all the returns (including the
+most recent) from the callback. These could be `result` or an `error` depending on what the callback
+returned at the time.
 
 ### `rerender`
 

Diff for: src/pure.js

@@ -21,25 +21,28 @@ function Fallback() {
 }
 
 function resultContainer() {
-  let value = null
-  let error = null
+  const results = []
   const resolvers = []
 
   const result = {
+    get all() {
+      return results.map(({ value, error }) => error || value)
+    },
     get current() {
+      const { value, error } = results[results.length - 1]
       if (error) {
         throw error
       }
       return value
     },
     get error() {
+      const { error } = results[results.length - 1]
       return error
     }
   }
 
-  const updateResult = (val, err) => {
-    value = val
-    error = err
+  const updateResult = (value, error) => {
+    results.push({ value, error })
     resolvers.splice(0, resolvers.length).forEach((resolve) => resolve())
   }
 
@@ -48,8 +51,8 @@ function resultContainer() {
     addResolver: (resolver) => {
       resolvers.push(resolver)
     },
-    setValue: (val) => updateResult(val),
-    setError: (err) => updateResult(undefined, err)
+    setValue: (value) => updateResult(value),
+    setError: (error) => updateResult(undefined, error)
   }
 }
 

Diff for: test/resultHistory.test.js

@@ -0,0 +1,34 @@
+import { renderHook } from '../src'
+
+describe('result history tests', () => {
+  let count = 0
+  function useCounter() {
+    const result = count++
+    if (result === 2) {
+      throw Error('expected')
+    }
+    return result
+  }
+
+  test('should capture all renders states of hook', () => {
+    const { result, rerender } = renderHook(() => useCounter())
+
+    expect(result.current).toEqual(0)
+    expect(result.all).toEqual([0])
+
+    rerender()
+
+    expect(result.current).toBe(1)
+    expect(result.all).toEqual([0, 1])
+
+    rerender()
+
+    expect(result.error).toEqual(Error('expected'))
+    expect(result.all).toEqual([0, 1, Error('expected')])
+
+    rerender()
+
+    expect(result.current).toBe(3)
+    expect(result.all).toEqual([0, 1, Error('expected'), 3])
+  })
+})