Re-introduced test/data directory

It was removed by accident in 171e9aae.
In e0fa4cd7, the file `test/data/.gitignore` was restored into `./.gitignore`
while that file effectively makes sure that git stores the `test/data` folder.

I tried to check whether `./.gitignore` was present before, but I couldn't find
one, so I assume this commit sets everything right.
Merge branch 'dataDirectory'