It's crazy how many weird bugs you can detect with such a trivial method.
For applications like a spreadsheet that have a million overlapping features, it's impossible to manually write unit tests for every combination of features, so randomized tests do a lot of heavy lifting.
If, of course, you can calculate rule 110/124, then your spread sheet can be considered Turing complete.
"With LAMBDA, Excel has become Turing-complete. You can now, in principle, write any computation in the Excel formula language.Jan 25, 2021"."
The only caveat to Excel being Turing-complete is that it will never ever display the results properly.
Maybe your spreadsheet will do better?
That strategy was also part of testing the original Mac. See https://www.folklore.org/Monkey_Lives.html.
As that article hunts at (“usually it didn't run for more than 20 minutes, even if it didn't crash, because the Monkey would invariably select the quit command”), there’s a black art in determining what “completely random” means.
You probably want the ability to change that depending on your testing needs. For example, if you’ve been working on the code for array formulas, the randomizer better create and edit them fairly frequently.
So the former finds crazy obscure edges, but the combinatorics make it less likely to hit any particular combination. The latter is the opposite. They pair really well.
Isn't the ability to interact with local environment, half the reason why people use Excel in the first place?
Okey maybe if they connect the cloud instance to a shared drive, that could indeed replace it
But you're right, there are people who really want local-only. We'll probably make a desktop app in the future.