add waitFor msg

API.md

@@ -294,6 +294,7 @@ interim DOM states (e.g. loading states, pending promises, etc).
 -   `options` **[Object](https://developer.mozilla.org/docs/Web/JavaScript/Reference/Global_Objects/Object)?** the options to be used (optional, default `{}`)
     -   `options.timeout` **[number](https://developer.mozilla.org/docs/Web/JavaScript/Reference/Global_Objects/Number)** the time to wait (in ms) for a match (optional, default `1000`)
     -   `options.count` **[number](https://developer.mozilla.org/docs/Web/JavaScript/Reference/Global_Objects/Number)** the number of elements that should match the provided selector (null means one or more) (optional, default `null`)
+    -   `options.timeoutMessage` **[string](https://developer.mozilla.org/docs/Web/JavaScript/Reference/Global_Objects/String)** the message to use in the reject on timeout (optional, default `'waitFor timed out'`)
 
 Returns **([Element](https://developer.mozilla.org/docs/Web/API/Element) \| [Array](https://developer.mozilla.org/docs/Web/JavaScript/Reference/Global_Objects/Array)<[Element](https://developer.mozilla.org/docs/Web/API/Element)>)** the element (or array of elements) that were being waited upon
 

addon-test-support/@ember/test-helpers/dom/wait-for.js

@@ -15,7 +15,10 @@ import { nextTickPromise } from '../-utils';
   @param {number} [options.count=null] the number of elements that should match the provided selector (null means one or more)
   @returns {Element|Array<Element>} the element (or array of elements) that were being waited upon
 */
-export default function waitFor(selector, { timeout = 1000, count = null } = {}) {
+export default function waitFor(
+  selector,
+  { timeout = 1000, count = null, timeoutMessage = 'waitFor timed out' } = {}
+) {
   return nextTickPromise().then(() => {
     if (!selector) {
       throw new Error('Must pass a selector to `waitFor`.');
@@ -32,6 +35,6 @@ export default function waitFor(selector, { timeout = 1000, count = null } = {})
     } else {
       callback = () => getElement(selector);
     }
-    return waitUntil(callback, { timeout });
+    return waitUntil(callback, { timeout, timeoutMessage });
   });
 }

tests/unit/dom/wait-for-test.js

@@ -75,7 +75,19 @@ module('DOM Helper: waitFor', function(hooks) {
     } catch (error) {
       let end = Date.now();
       assert.ok(end - start >= 100, 'timed out after correct time');
-      assert.equal(error.message, 'waitUntil timed out');
+      assert.equal(error.message, 'waitFor timed out');
+    }
+  });
+
+  test('wait for selector with timeoutMessage', async function(assert) {
+    assert.expect(1);
+
+    await setupContext(context);
+
+    try {
+      await waitFor('.something', { timeoutMessage: '.something timed out' });
+    } catch (error) {
+      assert.equal(error.message, '.something timed out');
     }
   });
 });