Mastering Rust - Second Edition

Isolating test code

When our tests grow in complexity, there may be additional helper methods that we might create that only gets used within the context of our test code. In such situations, it is beneficial to isolate the test-related code from the actual code. We can do this by encapsulating all of our test-related code inside a module and putting a #[cfg(test)] annotation over it.

The cfg in the #[cfg(...)] attribute is generally used for conditional compilation and not just limited to test code. It can include or exclude code for different architectures or configuration flags. Here, the configuration flag is test. You might remember that the tests in the previous chapter were already using this form. This has the advantage that your ...