Tests don't pass in clean checkout

[vorner]

Steps to reproduce:

• Make a clean checkout of this repository (without Cargo.lock).
• Run cargo test.

I'm getting compile errors (cannot find macro prop_oneof) from the test.

I suspect this is due to incompatible version of proptest. However, it is unclear which version is compatible, since the Cargo.toml doesn't restrict it properly and the repository doesn't contain Cargo.lock.