[FRAME] Executive invariant fuzzer

[ggwpez]

Adding some stuff to Executive in #3666 and there are now so many assumptions of what comes first and stuff being done in the correct order.

Would be nice to have a dedicated fuzzer crate that applies a random number of inherents+transactions and then asserts event records, similar to this test:

polkadot-sdk/substrate/frame/executive/src/tests.rs

Line 1378 in 8e0bca6

for (n_in, n_tx) in (0..15usize).zip(0..15usize) {

[gitofdeepanshu]

can I take this?

[ggwpez]

Yea sure @gitofdeepanshu!

I think the paged-list fuzzer should give a good example for this: https://github.com/paritytech/polkadot-sdk/blob/daa9ecf77d03bdc80282b9c63e0a1eee136dd2bc/substrate/frame/paged-list/fuzzer/src/paged_list.rs

[gitofdeepanshu]

Hey @ggwpez
I need some advice,
My plan was to create a fuzzer crate that would just do

fn main() {
	loop {
		fuzz!(|data: (usize, usize, bool)| {
			callbacks_in_block_execution_works_inner(data.0, data.1, data.2);
		});
	}
}

and just modify the same function that you linked above.

The problem is I would need the mock runtime's functions and structs that you created in the test folder, but it is behind #[cfg(test)] feature and uses dev-dependencies which mean I can't import the mock runtime and some other required functions. (or can I?)

AFAIK we can either create a new mock runtime in fuzzer crate or (just for the duration of test) manually modify the pallet-executive, remove the dev-dependencies and 'test' feature flag, import all the required code in fuzzer crate, test it and change the code back to normal.

Kindly guide what should be the best step here.

[ggwpez]

@gitofdeepanshu yea it looks like we would either need to duplicate the code or import it.
I think it should be fine to guard the mock runtime + pallets behind cfg(feature = "std") instead of cfg(test) to avoid duplicating everything.
It should not be to big of a code change and should remove most dev-dependencies.

Otherwise it would also be possible to use the substrate-test-runtime crate, but it does not have all these nice pallets with assertions deployed.