SQL sensor (#12142)

* Initial Commit

* Passed all checks

* Make DB_URL required

* addresses review comments from @fabaff

* unused variable

tests/components/sensor/test_sql.py

@@ -0,0 +1,37 @@
+"""The test for the sql sensor platform."""
+import unittest
+
+from homeassistant.setup import setup_component
+
+from tests.common import get_test_home_assistant
+
+
+class TestSQLSensor(unittest.TestCase):
+    """Test the SQL sensor."""
+
+    def setUp(self):
+        """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_query(self):
+        """Test the SQL sensor."""
+        config = {
+            'sensor': {
+                'platform': 'sql',
+                'db_url': 'sqlite://',
+                'queries': [{
+                    'name': 'count_tables',
+                    'query': 'SELECT count(*) value FROM sqlite_master;',
+                    'column': 'value',
+                }]
+            }
+        }
+
+        assert setup_component(self.hass, 'sensor', config)
+
+        state = self.hass.states.get('sensor.count_tables')
+        self.assertEqual(state.state, '0')