Adds light switch platform (#18562)

* Adds light switch platform

* Addresses HoundCI warnings

* Addresses Flake8 reported issues

* Removes async_update call as per review

tests/components/light/test_switch.py

@@ -0,0 +1,81 @@
+"""The tests for the Light Switch platform."""
+
+from homeassistant.setup import async_setup_component
+from tests.components.light import common
+from tests.components.switch import common as switch_common
+
+
+async def test_default_state(hass):
+    """Test light switch default state."""
+    await async_setup_component(hass, 'light', {'light': {
+        'platform': 'switch', 'entity_id': 'switch.test',
+        'name': 'Christmas Tree Lights'
+    }})
+    await hass.async_block_till_done()
+
+    state = hass.states.get('light.christmas_tree_lights')
+    assert state is not None
+    assert state.state == 'unavailable'
+    assert state.attributes['supported_features'] == 0
+    assert state.attributes.get('brightness') is None
+    assert state.attributes.get('hs_color') is None
+    assert state.attributes.get('color_temp') is None
+    assert state.attributes.get('white_value') is None
+    assert state.attributes.get('effect_list') is None
+    assert state.attributes.get('effect') is None
+
+
+async def test_light_service_calls(hass):
+    """Test service calls to light."""
+    await async_setup_component(hass, 'switch', {'switch': [
+        {'platform': 'demo'}
+    ]})
+    await async_setup_component(hass, 'light', {'light': [
+        {'platform': 'switch', 'entity_id': 'switch.decorative_lights'}
+    ]})
+    await hass.async_block_till_done()
+
+    assert hass.states.get('light.light_switch').state == 'on'
+
+    common.async_toggle(hass, 'light.light_switch')
+    await hass.async_block_till_done()
+
+    assert hass.states.get('switch.decorative_lights').state == 'off'
+    assert hass.states.get('light.light_switch').state == 'off'
+
+    common.async_turn_on(hass, 'light.light_switch')
+    await hass.async_block_till_done()
+
+    assert hass.states.get('switch.decorative_lights').state == 'on'
+    assert hass.states.get('light.light_switch').state == 'on'
+
+    common.async_turn_off(hass, 'light.light_switch')
+    await hass.async_block_till_done()
+
+    assert hass.states.get('switch.decorative_lights').state == 'off'
+    assert hass.states.get('light.light_switch').state == 'off'
+
+
+async def test_switch_service_calls(hass):
+    """Test service calls to switch."""
+    await async_setup_component(hass, 'switch', {'switch': [
+        {'platform': 'demo'}
+    ]})
+    await async_setup_component(hass, 'light', {'light': [
+        {'platform': 'switch', 'entity_id': 'switch.decorative_lights'}
+    ]})
+    await hass.async_block_till_done()
+
+    assert hass.states.get('light.light_switch').state == 'on'
+
+    switch_common.async_turn_off(hass, 'switch.decorative_lights')
+    await hass.async_block_till_done()
+
+    assert hass.states.get('switch.decorative_lights').state == 'off'
+    assert hass.states.get('light.light_switch').state == 'off'
+
+    switch_common.async_turn_on(hass, 'switch.decorative_lights')
+    await hass.async_block_till_done()
+
+    assert hass.states.get('switch.decorative_lights').state == 'on'
+    assert hass.states.get('light.light_switch').state == 'on'