Fuzzing for XCM & Integration Tests

[ghzlatarev]

Adding a degree of randomization in Manta's testing can be beneficial to catch more bugs.
Use manta-pay's test randomization as reference.

[Garandor]

Check out what Brandon did in manta-pay pallet ( manual randomization, no framework )

[Dengjianping]

Maybe we can try this tool https://github.com/rust-fuzz/cargo-fuzz
Seems it's a solid tool which is being used by like wasmtime.
And lots of bugs are found by it: https://github.com/rust-fuzz/trophy-case

Here's the doc: https://rust-fuzz.github.io/book/introduction.html

There's another alternative for fuzzing test: https://crates.io/crates/honggfuzz

[Dengjianping]

And seems substrate has some ideas on fuzzing test.
paritytech/polkadot-sdk#251