Improve dimmer support (#62)

* discover dimmers properly

* fix circular import, hopefully

* add is_color to SmartDevice API

* allow changing the dimming without implicitly turning the device on

* Add tests for device type handling for discovery data, make sure new fixtures are added to categories inside conftest

kasa/tests/test_discovery.py

@@ -0,0 +1,43 @@
+# type: ignore
+import pytest  # type: ignore # https://github.com/pytest-dev/pytest/issues/3342
+
+from kasa import DeviceType, Discover, SmartDevice, SmartDeviceException
+
+from .conftest import bulb, dimmer, plug, strip
+
+# to avoid adding this for each async function separately
+pytestmark = pytest.mark.asyncio
+
+
+@plug
+async def test_type_detection_plug(dev: SmartDevice):
+    d = Discover._get_device_class(dev.protocol.discovery_data)("localhost")
+    assert d.is_plug
+    assert d.device_type == DeviceType.Plug
+
+
+@bulb
+async def test_type_detection_bulb(dev: SmartDevice):
+    d = Discover._get_device_class(dev.protocol.discovery_data)("localhost")
+    assert d.is_bulb
+    assert d.device_type == DeviceType.Bulb
+
+
+@strip
+async def test_type_detection_strip(dev: SmartDevice):
+    d = Discover._get_device_class(dev.protocol.discovery_data)("localhost")
+    assert d.is_strip
+    assert d.device_type == DeviceType.Strip
+
+
+@dimmer
+async def test_type_detection_dimmer(dev: SmartDevice):
+    d = Discover._get_device_class(dev.protocol.discovery_data)("localhost")
+    assert d.is_dimmer
+    assert d.device_type == DeviceType.Dimmer
+
+
+async def test_type_unknown():
+    invalid_info = {"system": {"get_sysinfo": {"type": "nosuchtype"}}}
+    with pytest.raises(SmartDeviceException):
+        Discover._get_device_class(invalid_info)