Enable checkstyle on test sources

[brenuart]

I also noticed that checkstyle is not enabled on test sources...

I think we should enable it as well, at least to avoid issues with checkstyle integration in IDEs. I could not find a way to configure the Eclipse plugin to ignore test sources. This gives me quite a lot of warnings :(

Not so much issues tho, mostly "file does not end with a new line" and "trailing white spaces".