Pytest tests (#17750)

* Convert core tests

* Convert component tests to use pytest assert

* Lint 🤷‍♂️

* Fix test

* Fix 3 typos in docs

tests/components/sensor/test_sql.py

@@ -61,4 +61,4 @@ class TestSQLSensor(unittest.TestCase):
         assert setup_component(self.hass, 'sensor', config)
 
         state = self.hass.states.get('sensor.count_tables')
-        self.assertEqual(state.state, STATE_UNKNOWN)
+        assert state.state == STATE_UNKNOWN