For balance, as threads like this will always get responses about the tests being agonising and intrusive, I think that it's valuable to include other experiences - like mine last year (my first - which was a Happy Birthday letter from the NHS that I hadn't expected).
I expected it to takes ages, be incredibly painful, etc, etc, as that's what you read about.
The screening room was in an ancient section of the 'used to be a hospital, is now used as a site for any random things the Trust can't fit anywhere else' site. Got inside once I'd found it (follow a painted line taking me past the bins at the back of the carpark). There wasn't anybody else waiting, as a lot or women just don't turn up - probably expecting agonising assaults by machine or something like that if they've read posts online.
Got invited into the room and asked to take my top off and walk to the machine. She then said she needed to lift me, gave me time to adjust my shoulder and then went to take the first image, etc, etc. There was no painful squishing, it felt cold, obviously, but it was more like the machine held the tissue, not anything more than that and a slight sensation of almost pulling on the skin where my breasts meet my body. Repeat for the other side, get dressed and go.
Then I got the results a couple of weeks later. Incredibly easy, not painful at all, incredibly quick and potentially lifesaving. But how many women that did not attend on the basis of 'knowing' it's going to be awful have missed a test that wasn't in my experience as portrayed (and I genuinely expected) might have had something that would have shown up?