Add sensor_class to binary_sensor

This adds a 'sensor_class' property and attribute, which should be either
None or one of several defined SENSOR_CLASSES to indicate contextual
information about what the sensor is measuring.

tests/components/binary_sensor/test_binary_sensor.py

@@ -0,0 +1,36 @@
+"""
+tests.components.binary_sensor.test_binary_sensor
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+Test the binary_sensor base class
+"""
+import unittest
+from unittest import mock
+
+from homeassistant.components import binary_sensor
+from homeassistant.const import STATE_ON, STATE_OFF
+
+
+class TestBinarySensor(unittest.TestCase):
+    def test_state(self):
+        sensor = binary_sensor.BinarySensorDevice()
+        self.assertEqual(STATE_OFF, sensor.state)
+        with mock.patch('homeassistant.components.binary_sensor.'
+                        'BinarySensorDevice.is_on',
+                        new=False):
+            self.assertEqual(STATE_OFF,
+                             binary_sensor.BinarySensorDevice().state)
+        with mock.patch('homeassistant.components.binary_sensor.'
+                        'BinarySensorDevice.is_on',
+                        new=True):
+            self.assertEqual(STATE_ON,
+                             binary_sensor.BinarySensorDevice().state)
+
+    def test_attributes(self):
+        sensor = binary_sensor.BinarySensorDevice()
+        self.assertEqual({'sensor_class': None},
+                         sensor.device_state_attributes)
+        with mock.patch('homeassistant.components.binary_sensor.'
+                        'BinarySensorDevice.sensor_class',
+                        new='motion'):
+            self.assertEqual({'sensor_class': 'motion'},
+                             sensor.device_state_attributes)