feat(waitFor): improve error message for non-function callbacks

src/__tests__/wait-for.js

@@ -1,3 +1,4 @@
+import {renderIntoDocument} from './helpers/test-utils'
 import {waitFor} from '../'
 
 test('waits callback to not throw an error', async () => {
@@ -32,3 +33,13 @@ test('uses generic error if there was no last error', async () => {
   ).catch(e => e)
   expect(result).toMatchInlineSnapshot(`[Error: Timed out in waitFor.]`)
 })
+
+test('throws nice error if provided callback is not a function', () => {
+  const {queryByTestId} = renderIntoDocument(`
+    <div data-testid="div"></div>
+  `)
+  const someElement = queryByTestId('div')
+  expect(() => waitFor(someElement)).toThrow(
+    'Received `callback` arg must be a function',
+  )
+})

src/wait-for.js

@@ -22,6 +22,10 @@ function waitFor(
     },
   } = {},
 ) {
+  if (typeof callback !== 'function') {
+    throw new TypeError('Received `callback` arg must be a function')
+  }
+
   // created here so we get a nice stacktrace
   const timedOutError = new Error('Timed out in waitFor.')
   if (interval < 1) interval = 1