Q: Can I test FFADO without having a device?
A: Yes and No. Yes you can test whether FFADO is installed properly and whether jack can use it. No, without a device you can't really test it.
As a first step try and get jack running with ALSA first, such that you have some experience with jack as a system.
Make sure the "raw1394" kernel module is loaded (sudo modprobe raw1394). Don't load the jack GUI, but open up a terminal and run: "jackd -R -d firewire -v4". There should be a line like this:
... Fatal (ffado.cpp)[ 167] ffado_streaming_init: There are no devices on the bus
If you have this line, your system is configured correctly. The firewire backend of jack is loaded, and it has scanned the bus for devices, but didn't find any.