At the moment I'm writing tests and think about to export all File-I/O-Operations into separate threads within my GUI-App, because I fear that a large file can block the main-thread. This wouldn't be user-friendly.
Its common to export File-I/O-Operations into separate worker-threads?
Well, it depends, but generally it is a very good idea. If your main thread is your event pump, then yes; it is highly recommended to execute lengthy operations in separate threads. Particularly if the app is using a slow GPRS/3G connection, you typically don't want the app to block when using the network. Local file operations can occasionally be quite slow as well, depending on how busy the device is.
The Java Swing Worker model is an example of how to do this in a modular and thread-safe way. I suggest you study it for inspiration as it is well documented. Then again, I am sure Android has similar facilities for executing code outside the main thread.
If you are writing (unit) tests for it, I suggest establishing a pattern where you can inject your worker code as part of the test and keeping your I/O code strictly outside of context from the main thread. That way, you can simulate how the app behaves during slow connection without actually having to use the network at all.
