Given a region that has started inflating, and given the inflaton potential and the coupling of the inflaton to other matter, very detailed and unambiguous predictions can be made about the initial conditions of the SBB epoch that follows inflation. The catch is that at the moment we do not have a unique candidate for the inflaton and furthermore we are pretty confused in general about physics at the relevant energy scales.
Despite these uncertainties inflation makes a pretty powerful set of predictions. I will discuss these predictions here, but first it is worth discussing just what one might mean by ``powerful'' predictions. From time to time informal discussions of inflation degenerate into a debate about whether inflation will ever really be tested. The uncertainties about the inflaton mentioned above are the reason such debates can exist. As long as there is no single theory being tested, there is ``wiggle room'' for the theory to bend and adapt to pressure from the data.
Today there are certain broad expectations of what the inflaton sector might look like, and despite their breadth, these expectations lead to a set of highly testable predictions. However, radical departures from these broad expectations are also possible, and some will argue that such departures mean that one is never really testing inflation.
I have little patience for these arguments. The fundamental currency of scientific progress is the confirmation or rejections of specific ideas. There is no question that the standard picture of cosmic inflation commits itself to very specific predictions. To the extent that any one of these predictions is falsified, a real revolution will have to occur in our thinking. Furthermore, since most of these tests will be realized in the foreseeable future, the testing of inflation is not a philosophical question. It is a very real part of the field of cosmology.
To be absolutely clear on this matter, I have indicated in each topic below both the predictions of the standard picture and the possible exotic variations.