Rust by Example

Sometimes there is a need to have dependencies for tests (or examples, or benchmarks) only. Such dependencies are added to Cargo.toml in the [dev-dependencies] section. These dependencies are not propagated to other packages which depend on this package.

One such example is using a crate that extends standard assert! macros. File Cargo.toml:

# standard crate data is left out

[dev-dependencies]

pretty_assertions = "0.4.0"

File src/lib.rs:

// externing crate for test-only use

#[cfg(test)]

#[macro_use]

extern crate pretty_assertions;

pub fn add(a: i32, b: i32) -> i32 {

a + b

}

#[cfg(test)]

mod tests {

use super::*;

#[test]

fn test_add() {

assert_eq!(add(2, 3), 5);

}

}

See Also

Cargo docs on specifying dependencies.