I'll give you the good example I've been doing for the last two decades: testing a compiler. The complexity here is the complete opposite of the simple toy exa

I'll give you the good example I've been doing for the last two decades: testing a compiler. The complexity here is the complete opposite of the simple toy examples. What are the edge cases of an optimizing compiler? How do you even approach them, if they're buried deep in a chain of transformations? The properties are simple things like "the compiler shouldn't crash, the compiled code shouldn't crash, and code compiled with different optimization levels should do the same thing." This assumes the randomly generated code doesn't touch undefined behavior in the language spec. Here's a recent example of a bug found by this approach. The Common Lisp code stimulating the bug has been automatically minimized: https://bugs.launchpad.net/sbcl/+bug/2109837 https://bugs.launchpad.net/sbcl/+bug/2109837 with the bug fix https://sourceforge.net/p/sbcl/sbcl/ci/1abebf7addda1a43d6d24fa8d1d7eefd36a7b3af/ https://sourceforge.net/p/sbcl/sbcl/ci/1abebf7addda1a43d6d24...