Implement unit testing

[AaronLionsheep]

There should be unit tests created for Each Shelly device class. Using GitHub automatons, pull requests from other developers can run these same tests to ensure no bugs are inadvertently introduced.

This will require "mock" indigo devices and a broker device. Unit tests can use these mocking classes to interact with Shelly devices.

• [x] Shelly
• [x] Shelly 1
• [x] Shelly 1PM
• [x] Shelly 2.5
• [x] Shelly 4 Pro
• [x] Shelly Dimmer/SL
• [x] Shelly EM Relay
• [x] Shelly EM Meter
• [x] Shelly 3EM Meter
• [x] Shelly RGBW2 (white)
• [x] Shelly RGBW2 (color)
• [x] Shelly HT
• [x] Shelly Flood
• [x] Shelly Door/Window
• [x] Shelly Bulb
• [x] Shelly Bulb Vintage
• [x] Shelly Bulb Duo
• [x] Shelly Plug
• [x] Shelly PlugS
• [x] Shelly Add-on DS1820
• [x] Shelly Add-on DHT22
• [x] Shelly Add-on Detached Switch

[AaronLionsheep]

https://medium.com/swlh/automate-python-testing-with-github-actions-7926b5d8a865

[AaronLionsheep]

All devices have tests now.