Adding basic CI tests

[ghost]

It seems master is broken every once in a while. I suggest adding some basic integration tests. Something like:

1. Goal: Write X into a file
2. Goal: Open file and echo the content

I know this is not easy as there are costs involved, but we could use 3.5 for this and improve reliability of master branch. WDYT?

[rickythefox]

The existing tests already require a valid key to be set, even if they are called "unit tests" they are actually integration tests. Not sure how this is to be handled as I assume no one wants to pay the bills for running tests?