How to call functions that aren't inside a mod

Question

These are the contents of my src/lib.rs file:

pub fn foo() {}

#[cfg(test)]
mod tests {
    #[test]
    fn it_works() {
        foo();
    }
}

When I run cargo test, I get the following error:

error[E0425]: cannot find function `foo` in this scope
 --> src/lib.rs:7:9
  |
7 |         foo();
  |         ^^^ not found in this scope

How do I call foo from inside the test module?

Answer 1

You could use super:: to refer to the parent module:

fn it_works() {
    super::foo();
}

In Rust 2015, you can use :: to refer to the root module of the crate:

fn it_works() {
    ::foo();
}

In Rust 2018, you can use crate:: to refer to the root module of the crate:

fn it_works() {
    crate::foo();
}

Or, as foo may be used repeatedly, you could use it in the module:

mod tests {
    use foo;         // <-- import the `foo` from the root module
    // or
    use super::foo;  // <-- import the `foo` from the parent module

    fn it_works() {
        foo();
    }
}

For test modules, it's also common to import everything from the parent module:

mod tests {
    use super::*;  // <-- import everything from the parent module

    fn it_works() {
        foo();
    }
}