Initializing statistics sensor with data from database (#9753)

* Initializing statistics sensor with data from database

* fixed broken test case

* usage of recorder component is now optional, thx to @andrey-git

* added test case for initialize_from_database

tests/components/sensor/test_statistics.py

@@ -8,6 +8,8 @@ from homeassistant.util import dt as dt_util
 from tests.common import get_test_home_assistant
 from unittest.mock import patch
 from datetime import datetime, timedelta
+from tests.common import init_recorder_component
+from homeassistant.components import recorder
 
 
 class TestStatisticsSensor(unittest.TestCase):
@@ -135,3 +137,28 @@ class TestStatisticsSensor(unittest.TestCase):
 
         self.assertEqual(6, state.attributes.get('min_value'))
         self.assertEqual(14, state.attributes.get('max_value'))
+
+    def test_initialize_from_database(self):
+        """Test initializing the statistics from the database."""
+        # enable the recorder
+        init_recorder_component(self.hass)
+        # store some values
+        for value in self.values:
+            self.hass.states.set('sensor.test_monitored', value,
+                                 {ATTR_UNIT_OF_MEASUREMENT: TEMP_CELSIUS})
+            self.hass.block_till_done()
+        # wait for the recorder to really store the data
+        self.hass.data[recorder.DATA_INSTANCE].block_till_done()
+        # only now create the statistics component, so that it must read the
+        # data from the database
+        assert setup_component(self.hass, 'sensor', {
+            'sensor': {
+                'platform': 'statistics',
+                'name': 'test',
+                'entity_id': 'sensor.test_monitored',
+                'sampling_size': 100,
+            }
+        })
+        # check if the result is as in test_sensor_source()
+        state = self.hass.states.get('sensor.test_mean')
+        self.assertEqual(str(self.mean), state.state)