Integration Tests

my_project/
  src/
    lib.rs
  tests/
    integration_test.rs

pub fn add_two(n: i32) -> i32 {
    n + 2
}

// In tests/integration_test.rs this would look like:
// use my_project::add_two;
// #[test]
// fn test_add_two() {
//     assert_eq!(add_two(3), 5);
// }

fn main() {
    println!("add_two(3) = {}", add_two(3));
}

fn parse_and_double(input: &str) -> Option<i32> {
    input.parse::<i32>().ok().map(|n| n * 2)
}

fn main() {
    println!("{:?}", parse_and_double("21"));
    println!("{:?}", parse_and_double("oops"));
}

cargo test

1. Placing integration tests inside src/ instead of the top-level tests/ directory, which Cargo treats differently.
2. Forgetting integration tests can only call a crate's public API, not its private internal functions.
3. Assuming a single tests/ file covers everything -- Cargo compiles each file in tests/ as its own separate test binary.

• Integration tests live in a top-level tests/ directory, separate from src/.
• Each file in tests/ is compiled as an independent crate that can only access the library's public API.
• Integration tests verify that multiple parts of a library work correctly together, from an external caller's perspective.
• cargo test runs both unit tests (in src/) and integration tests (in tests/) together by default.