Macro harness

macro_rules! harness {
    ( $( { $($args:tt)* } ),+ $(,)* ) => { ... };
    ( $( $name:path, $root:expr, $pattern:expr ),+ $(,)* ) => { ... };
}

datatest-stable test harness entry point. Should be declared in the test module.

Also, harness should be set to false for that test module in Cargo.toml (see Configuring a target).