Add version sensor (#8912)

* Add version sensor

* Set version directly

* Rework tests and fix typo

* Remove additional blank line

tests/components/sensor/test_version.py

@@ -0,0 +1,50 @@
+"""The test for the version sensor platform."""
+import asyncio
+import unittest
+from unittest.mock import patch
+
+from homeassistant.setup import setup_component
+
+from tests.common import get_test_home_assistant
+
+MOCK_VERSION = '10.0'
+
+
+class TestVersionSensor(unittest.TestCase):
+    """Test the Version sensor."""
+
+    def setup_method(self, method):
+        """Set up things to be run when tests are started."""
+        self.hass = get_test_home_assistant()
+
+    def teardown_method(self, method):
+        """Stop everything that was started."""
+        self.hass.stop()
+
+    def test_version_sensor(self):
+        """Test the Version sensor."""
+        config = {
+            'sensor': {
+                'platform': 'version',
+            }
+        }
+
+        assert setup_component(self.hass, 'sensor', config)
+
+    @asyncio.coroutine
+    def test_version(self):
+        """Test the Version sensor."""
+        config = {
+            'sensor': {
+                'platform': 'version',
+                'name': 'test',
+            }
+        }
+
+        with patch('homeassistant.const.__version__', MOCK_VERSION):
+            assert setup_component(self.hass, 'sensor', config)
+            self.hass.block_till_done()
+
+        state = self.hass.states.get('sensor.test')
+
+        self.assertEqual(state.state, '10.0')