Attribute Macro test_with::runtime_file

#[runtime_file]

Run test case when the example running and the file exist.

 // write as example in exmaples/*rs
 test_with::runner!(file);
 #[test_with::module]
 mod file {
     #[test_with::runtime_file(/etc/hostname)]
     fn test_works() {
         assert!(true);
     }
 }