rust-testing.md

Proposal for more tooling to allow for custom testing harness:

• Initial - rust-lang/rfcs#816
• Extension to RFC - rust-lang/rfcs#2318

Newest coolest tools

• https://github.com/altsysrq/proptest
• https://github.com/mitsuhiko/insta
• https://github.com/utkarshkukreti/speculate.rs
• https://github.com/BurntSushi/quickcheck
• https://github.com/lipanski/mockito

More packages: https://crates.rs/development-tools/testing