Add new_device_discovered event (#4132)

tests/components/device_tracker/test_init.py

@@ -306,6 +306,24 @@ class TestComponentsDeviceTracker(unittest.TestCase):
         self.assertEqual(mock_see.call_count, 1)
         self.assertEqual(mock_see.call_args, call(**params))
 
+    def test_new_device_event_fired(self):
+        """Test that the device tracker will fire an event."""
+        self.assertTrue(setup_component(self.hass, device_tracker.DOMAIN,
+                                        TEST_PLATFORM))
+        test_events = []
+
+        def listener(event):
+            """Helper method that will verify our event got called."""
+            test_events.append(event)
+
+        self.hass.bus.listen("device_tracker_new_device", listener)
+
+        device_tracker.see(self.hass, 'mac_1', host_name='hello')
+        device_tracker.see(self.hass, 'mac_1', host_name='hello')
+
+        self.hass.block_till_done()
+        self.assertEqual(1, len(test_events))
+
     # pylint: disable=invalid-name
     def test_not_write_duplicate_yaml_keys(self):
         """Test that the device tracker will not generate invalid YAML."""