Macro undefined when test module is moved to a separate file

Question

I am writing a test for a macro I want to export. The test works as long as I keep my tests in a single file, but as soon as I put the tests module in a separate file, I get an error.

export/src/lib.rs

pub mod my_mod {
    #[macro_export]
    macro_rules! my_macro {
        ( $x:expr ) => { $x + 1 };
    }

    pub fn my_func(x: isize) -> isize {
        my_macro!(x)
    }
}

export/tests/lib.rs

#[macro_use]
extern crate export;

mod my_test_mod {
    use export::my_mod;

    #[test]
    fn test_func() {
        assert_eq!(my_mod::my_func(1), 2);
    }

    #[test]
    fn test_macro() {
        assert_eq!(my_macro!(1), 2);
    }
}

Running cargo test indicates that both tests passed. If I extract my_test_mod to a file it no longer compiles.

export/src/lib.rs

Unchanged

export/tests/lib.rs

#[macro_use]
extern crate export;

mod my_test_mod;

export/tests/my_test_mod.rs

use export::my_mod;

#[test]
fn test_func() {
    assert_eq!(my_mod::my_func(1), 2);
}

#[test]
fn test_macro() {
    assert_eq!(my_macro!(1), 2); // error: macro undefined: 'my_macro!'
}

This gives me an error that the macro is undefined.

Answer 1

The problem here is that you aren't compiling what you think you are compiling. Check it out:

$ cargo test --verbose
   Compiling export v0.1.0 (file:///private/tmp/export)
     Running `rustc --crate-name my_test_mod tests/my_test_mod.rs ...`

When you run cargo test, it assumes that every .rs file is a test to be run. It doesn't know that my_test_mod.rs should only be compiled as part of another test!

The easiest solution is to move your module to the other valid module location, in a separate directory: tests/my_test_mod/mod.rs. Cargo will not recursively look inside the directory for test files.