Writing Automated Tests¹

To run the tests:

$ cargo test --package automated-tests --lib -- tests --nocapture
   running 1 test

Lessons Learned

As this chapter is mostly code intensive, I'll leave that to lib.rs.

To avoid running tests in parallel, or to control the number of threads:

cargo test -- --test-threads=1

To show function output (i.e. println!'s):

cargo test -- --show-output

To run a single test by name:

cargo test smaller_cannot_hold_larger

To run a subset of tests by name:

cargo test smaller_

To ignore some tests unless specifically requested:

#[test]
#[ignore]
fn expensive_test() {}

# Runs only ignored tests.
cargo test -- --ignored

# Runs all tests, including ignored.
cargo test -- --include-ignored

Unit tests are written in the src directly with the code they are testing:

#[cfg(tests)]
mod tests {
  use super::*;

  #[test]
  fn it_works() {}
}

Integration tests are written in a directory next to src,, tests:

11-automated-tests
├── Cargo.lock
├── Cargo.toml
├── src
│   └── lib.rs
└── tests
    └── integration_test.rs

cargo test --test integration_test

As you add more integration tests, you'll want to create more files in tests/:

├── Cargo.lock
├── Cargo.toml
├── src
│   └── lib.rs
└── tests
    ├── common
    │   └── mod.rs
    └── integration_test.rs