I am currently in the process of writing a script for a film about time travel. The first draft is complete, I put it to one side, and am now redrafting. I know time travel is a much used narrative device, but I like to think mine is original. One of the major criticisms people have of time travel films is that there are too many paradoxes and plot holes. I’ve tried to avoid this, but there are certain puzzles to which I don’t have any answers. I don’t think, with a story about time travel, that it is possible to have zero defects, but it is important to bring it as close to zero as possible. I just thought it might be fun to discuss how a time travel machine would be tested.
So. Where do we begin? I’m keeping this vague, so there are no spoilers for my screenplay (should it ever be filmed).
As a time traveller
I want to be able to travel back in time
So that I can effect change
OK. So now, we need to drill down into the actual acceptance criteria.
Given that I have selected a time
When I initiate time travel
Then I should be taken back to the time in question
Bit vague here. As we all know, the earth spins, and whips round the Sun at an alarming rate. Let’s take travelling back 30 years. Where you are stood right now won’t be in the same place 30 years ago. I think. I’m not an astrophysicist. Also, if you were to calculate it so that you landed in the same place, the features of that place may well have changed. So, there is the possibility that between now and 30 years ago, a tree has been chopped down, a building knocked down, or number 28’s bin is still out. Doreen would get a right shock if she went to bring the bin in and there was a time traveller in there. With a banana peel on his head.
A big issue with time travel in films and other narrative media is that changes made in the past would have such an impact on the present that the conditions that led to the time travel are no longer possible. However, what test cases would you need to prevent this? There would be obvious ones, like not being able to kill yourself, or the inventor of the time machine. So, what cases would be required to stop this from happening? Are they too numerous to consider? As QAs/Testers, should we be telling the world that test coverage would be so low as to make time travel dangerous beyond acceptable levels? What would the test cases and acceptance criteria be?