Add a test (e.g. strandtest)

[TAKeanice]

I am interested in using this library, since it has a very clean and simple interface. If it worked it would be my preferred way of driving my pixels. Unfortunately, I could not get the library to drive my SK6812 pixels yet.
I have adapted a version of the strandtest from https://forum.arduino.cc/index.php?topic=364208.0 (using an array of rgbwValues, setting its values, and passing it to your library instead of calling strip.show). Getting the adaptation to compile was quite easy, but nothing happened. In its original state, the strandtest worked.
That is why I would ask for an example (e.g. an adapted strandtest) from you if you don´t mind.