Test network connection instead of special cases

[zner0L]

Right now, the code has several test branches, mainly to do with data ingestion. This makes it impossible to cover the whole codes with tests (and is also bad practice, because we do not test the actual code). We should therefore remove theses cases and instead switch to testing with a proper TCP server, e.g. using https://github.com/pytest-dev/pytest-tcpclient.

[jnnsbrr]

Yes sounds much better. I did not investigate much but wanted a quick (and dirty) solution. pytest-tcpclient sounds much leaner. I hope its doable and does not take to long to set it up with the current approach.