Where put utility-functions for test-code in Rust?

How and where would one write utility-code for test-functions in Rust?

For example, I have the following code defining a path where generated files can be placed:

fn gen_test_dir() -> tempdir::TempDir {                                        
    tempdir::TempDir::new_in(Path::new("/tmp"), "filesyncer-    tests").unwrap()   
} 

This function is defined in tests/lib.rs and is used in the tests in that file. However, I would also like to use this function in the unittests declared by #[test] located in the src/lib.rs.

Is this possible to achieve without compiling the utility-function into the non-test binary and without duplicating code?