test: simplify attr-for-value test

test/vaadin-combo-box-light.html

@@ -154,14 +154,6 @@
     describe('vaadin-combobox-light-attr-for-value', () => {
       let comboBox, customInput, ironInput, nativeInput;
 
-      function whenIronInputReady(ironInput, callback) {
-        if (ironInput.inputElement) {
-          callback();
-        } else {
-          ironInput.addEventListener('iron-input-ready', callback);
-        }
-      }
-
       beforeEach(() => {
         comboBox = fixture('combobox-light-attr-for-value');
         comboBox.items = ['foo', 'bar', 'baz'];
@@ -185,35 +177,27 @@
           expect(customInput.customValue).to.eql('foo');
         });
 
-        it('should bind the input value correctly when getting input', done => {
+        it('should bind the input value correctly when getting input', () => {
           // Empty string by default.
           expect(comboBox._inputElementValue).to.eql('');
           expect(customInput.customValue).to.eql('');
           expect(nativeInput.value).to.eql('');
 
-          // We need to wait until <iron-input> is ready before trying to input text
-          // into the input, otherwise the test will fail when iron-input throws
-          // an error in `_onInput` because it tries to read `inputElement.value`
-          // but `inputElement` may still be undefined because iron-input hasn't yet
-          // detected the slotted <input> element.
-          whenIronInputReady(ironInput, () => {
-            // Use a timeout to get out of "iron-input-ready" event context, otherwise
-            // any thrown error (e.g. failed assertion) will result in a huge obscure
-            // error message in Firefox without any info about the assertion failure.
-            setTimeout(() => {
-
-              // Simulate typing an option with a keyboard and confirming it via Enter
-              nativeInput.value = 'foo';
-              fire('input', nativeInput);
-              MockInteractions.pressAndReleaseKeyOn(nativeInput, 13, null, 'Enter');
-
-              expect(comboBox.value).to.eql('foo');
-              expect(comboBox._inputElementValue).to.eql('foo');
-              expect(customInput.customValue).to.eql('foo');
-
-              done();
-            }, 0);
-          });
+          // Make sure the slotted <input> has been detected by <iron-input>
+          // before trying to modify the value of the <input>.
+          // Otherwise iron-input will throw an error (in `_onInput`) because
+          // it tries to read `inputElement.value` but `inputElement` is still
+          // undefined.
+          ironInput._observer.flush();
+
+          // Simulate typing an option with a keyboard and confirming it via Enter
+          nativeInput.value = 'foo';
+          fire('input', nativeInput);
+          MockInteractions.pressAndReleaseKeyOn(nativeInput, 13, null, 'Enter');
+
+          expect(comboBox.value).to.eql('foo');
+          expect(comboBox._inputElementValue).to.eql('foo');
+          expect(customInput.customValue).to.eql('foo');
         });
       });
     });