Thanks! This is exactly what I’ve been looking for.
I think, with compare_past_trace and just a few lines of code, I can have a function that takes two git commits and returns a set of tests that will work on one but fail on the other. (I prefer work with runtest.jl instead of trying out code at the REPL, so this fits perfectly into my workflow.)
Regarding mutable arguments: It’d be great if there were an option to recursively copy everything, always, but using a hash table so that multiple copies of the same object are only stored once. (RAM is cheap these days.)