Zebra/book/src/dev/proptests.md

Randomised Property Testing in Zebra

Zebra uses the proptest crate for randomised property testing.

Most types in zebra-chain have an Arbitrary implementation, which generates randomised test cases.

We try to derive Arbitrary impls whenever possible, so that they automatically update when we make structural changes. To derive, add the following attribute to the struct or enum:

#[cfg_attr(any(test, feature = "proptest-impl"), derive(Arbitrary))]
struct Example(u32);

When we want to use those Arbitrary impls in proptests in other crates, we use the proptest-impl feature as a dev dependency:

1. in zebra-chain: make the Arbitrary impl depend on #[cfg(any(test, feature = "proptest-impl"))]
2. in the other crate: add zebra-chain as a dev dependency: zebra-chain = { path = "../zebra-chain", features = ["proptest-impl"] }

If we need to add another dependency as part of the proptest-impl feature:

1. Add the crate name to the list of crates in the proptest-impl features entry
2. Add the crate as an optional dependencies entry
3. Add the crate as a required dev-dependencies entry

For an example of these changes, see PR 2070.