Chapter 11.3 Filename: tests/common/mod.rs hidden lines cause an error

[ghost]

• I have checked the latest main branch to see if this has already been fixed
• I have searched existing issues and pull requests for duplicates

URL to the section(s) of the book with this problem: https://doc.rust-lang.org/book/ch11-03-test-organization.html

Description of the problem:
Copying the content of the tests/common.rs file (subsequently tests/common/mod.rs) from the book includes hidden lines:

#![allow(unused)]
fn main() {
pub fn setup() {
    // setup code specific to your library's tests would go here
}
}

The chapter tells the user to include this in the integration_test.rs file with mod common;
This is fine, however, running the test fails due to the scoping of the setup function within the block of fn main(). The error is:

cargo test                            302ms  Mon Jan 17 15:35:08 2022
   Compiling adder v0.1.0 (/Users/{PATH_TO_ADDER}/adder)
error[E0425]: cannot find function `setup` in module `common`
 --> tests/integration_test.rs:7:13
  |
7 |     common::setup();
  |             ^^^^^ not found in `common`

For more information about this error, try `rustc --explain E0425`.
error: could not compile `adder` due to previous error

Suggested fix:
The content of mod.rs should just be

#![allow(unused)]
pub fn setup() {
    // setup code specific to your library's tests would go here
}

[rosnfeld]

Yes, I just hit this issue as well. I think the include of mod.rs needs a noplayground option set, which would stop it from having a main added and from it being runnable.