Fully polyfill KeyEvent so that you can programmatically create your own "keyboard" events.

tests/html/keyboard_event_test.dart

 library KeyboardEventTest;
 import '../../pkg/unittest/lib/unittest.dart';
 import '../../pkg/unittest/lib/html_config.dart';
 import 'dart:html';
 
 // Test that we are correctly determining keyCode and charCode uniformly across
 // browsers.
 
 main() {
 
   useHtmlConfiguration();
 
   keydownHandlerTest(KeyEvent e) {
     expect(e.charCode, 0);
   }
 
   test('keyboardEvent constructor', () {
     var event = new KeyboardEvent('keyup');
   });
   test('keys', () {
     // This test currently is pretty much a no-op because we
     // can't (right now) construct KeyboardEvents with specific keycode/charcode
     // values (a KeyboardEvent can be "init"-ed but not all the information can
     // be programmatically populated. It exists as an example for how to use
     // KeyboardEventController more than anything else.
-    KeyboardEventStream.onKeyDown(document.body).listen(
+    var subscription = KeyboardEventStream.onKeyDown(document.body).listen(
         keydownHandlerTest);
-    KeyEvent.keyDownEvent.forTarget(document.body).listen(keydownHandlerTest);
-    document.body.onKeyDown.listen((e) => print('regular listener'));
+    var subscription2 = KeyEvent.keyDownEvent.forTarget(document.body).listen(
+        keydownHandlerTest);
+    var subscription3 = document.body.onKeyDown.listen(
+        (e) => print('regular listener'));
+    subscription.cancel();
+    subscription2.cancel();
+    subscription3.cancel();
+  });
+
+  test('constructKeyEvent', () {
+    var stream = KeyEvent.keyPressEvent.forTarget(document.body);
+    var subscription = stream.listen((keyEvent) {
+      expect(keyEvent.charCode, 97);
+      expect(keyEvent.keyCode, 65);
+    });
+    var k = new KeyEvent('keypress', keyCode: 65, charCode: 97);
+    stream.add(k);
+    subscription.cancel();
+    // Capital "A":
+    stream.add(new KeyEvent('keydown', keyCode: 16, charCode: 0));
+
+    subscription = stream.listen((keyEvent) {
+      expect(keyEvent.charCode, 65);
+      expect(keyEvent.keyCode, 65);
+    });
+    stream.add(new KeyEvent('keypress', keyCode: 65, charCode: 65));
+    subscription.cancel();
+  });
+
+  test('KeyEventSequence', () {
+    // Press "?" by simulating "shift" and then the key that has "/" and "?" on
+    // it.
+    var streamDown = KeyEvent.keyDownEvent.forTarget(document.body);
+    var streamPress = KeyEvent.keyPressEvent.forTarget(document.body);
+    var streamUp = KeyEvent.keyUpEvent.forTarget(document.body);
+
+    var subscription = streamDown.listen((keyEvent) {
+      expect(keyEvent.keyCode, isIn([16, 191]));
+      expect(keyEvent.charCode, 0);
+    });
+
+    var subscription2 = streamPress.listen((keyEvent) {
+      expect(keyEvent.keyCode, 23);
+      expect(keyEvent.charCode, 63);
+    });
+
+    var subscription3 = streamUp.listen((keyEvent) {
+      expect(keyEvent.keyCode, isIn([16, 191]));
+      expect(keyEvent.charCode, 0);
+    });
+
+    streamDown.add(new KeyEvent('keydown', keyCode: 16, charCode: 0));
+    streamDown.add(new KeyEvent('keydown', keyCode: 191, charCode: 0));
+
+    streamPress.add(new KeyEvent('keypress', keyCode: 23, charCode: 63));
+
+    streamUp.add(new KeyEvent('keyup', keyCode: 191, charCode: 0));
+    streamUp.add(new KeyEvent('keyup', keyCode: 16, charCode: 0));
+    subscription.cancel();
+    subscription2.cancel();
+    subscription3.cancel();
   });
 }