Integration testing

  • Unit tests are testing one module in isolation at a time: they’re small and can test private code.
  • Integration tests are external to your crate and use only its public interface in the same way any other code would.
  • Their purpose is to test that many parts of your library work correctly together.

Cargo looks for integration tests in tests directory next to src.

File src/lib.rs:

 
// Define this in a crate called `adder`.
pub fn add(a: i32, b: i32) -> i32 {
    a + b
}

File with test: tests/integration_test.rs:

 
#[test]
fn test_add() {
    assert_eq!(adder::add(3, 2), 5);
}

Running tests with cargo test command:

 
$ cargo test
running 0 tests

test result: ok. 0 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out

     Running target/debug/deps/integration_test-bcd60824f5fbfe19

running 1 test
test test_add ... ok

test result: ok. 1 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out

   Doc-tests adder

running 0 tests

test result: ok. 0 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out
  1. Each Rust source file in the tests directory is compiled as a separate crate.
  2. In order to share some code between integration tests we can make a module with public functions, importing and using it within tests.

File tests/common/mod.rs:

 
pub fn setup() {
    // some setup code, like creating required files/directories, starting
    // servers, etc.
}

File with test: tests/integration_test.rs

 
// importing common module.
mod common;

#[test]
fn test_add() {
    // using common code.
    common::setup();
    assert_eq!(adder::add(3, 2), 5);
}
  • Creating the module as tests/common.rs also works
  • but is not recommended because the test runner will treat the file as a test crate and try to run tests inside it.