I'm no expert on basal testing, @MrBloominggrumpy but there are people here who are. You could do a search and read some threads. I have a pump so it's slightly different for me. But basically even if a person with diabetes didn't eat, their blood sugar would rise. The basal/background/slow insulin controls this. If you never ate, it should keep your blood sugar level. The bolus/fast insulin just deals with your food.
(FYI, the reason people don't just say fast and slow insulin is that when people are on a pump they only have fast insulin in it. This fast insulin does both jobs and acts as a basal/background and as a bolus/meal insulin. I hope that hasn't confused things mentioning that)
(FYI, the reason people don't just say fast and slow insulin is that when people are on a pump they only have fast insulin in it. This fast insulin does both jobs and acts as a basal/background and as a bolus/meal insulin. I hope that hasn't confused things mentioning that)