Code shared from the Rust Playground

playground.rs

macro_rules! test_cases {
    (@ [ :: $variant:ident :: stream :: compress ]) => {
        #[test] fn a() { }
    };

    (@ [ :: $variant:ident :: futures :: write :: compress ]) => {
        #[test] fn b() { }
    };

    (@ [ :: $variant:ident :: futures :: write :: decompress ]) => {
        #[test] fn c() { }
    };

    // expansions, generating a `mod $ident { }` around each level

    ($variant:ident) => {
        test_cases!($variant::{stream::compress, futures::write::{compress, decompress}});
    };
}

test_cases!(foobar);

// mod foobar {
//     mod stream {
//         mod compress {
//             #[test] fn a() {}
//         }
//     }
//     mod futures {
//         mod write {
//             mod compress {
//                 #[test] fn b() {}
//             }
//             mod decompress {
//                 #[test] fn c() {}
//             }
//         }
//     }
// }