I'm glad people are sharing their "test" workflows here. It's giving me ideas to refine how I do things and it's just plain interesting to see how others do stuff... especially the more experienced folks.
One thing I did a while back that I haven't really messed with in a while but intend to return to is this...
I created a project with a drum sim, an instance of Zeta with a realistic generic bass sound (Alembic Bass preset if anyone is interested but it could be anything... the Studio Instruments bass would probably be a good, simple choice for this) and blank guitar track.
In the MIDI bass track I programmed in some blues, jazz, rock and song specific bass parts. Mostly just 4/4 stuff like 12 bar blues, simple jazz progressions, etc and I actually put in the bassline for Little Wing because I just like jamming over that. All these progressions are in the track's take lanes and I've set the clips up so there is one full revolution of the whole progressions. I set the MIDI clips up as Groove Clips.
So now I can decide what I want to jam over (this is essentially to work on guitar improvisation), solo the lane that contains the bass progression, drag in an appropriate MIDI drum loop into the drum track and then just create loop points that span the whole progression.
I then jam into the guitar track with whatever sim/sound I want for however long I want. I can easily change the tempo (obviously) but in the MIDI bass track I can just use the track's transpose control to easily play in any key I want.
If I want to actually record something to use all I have to do is drag out the bass and drum groove clips to the length I want and disable looping and record the guitar part. That clip can be inserted into anything I want afterward or I can just do a Save As and have a new project on the go.
As I find new progressions I want to try out or write stuff I can just add an extra lane to the MIDI bass track.
Instant backup band to jam with.
Cheers.