Macro test_field

macro_rules! test_field {
    ($t:ident, $field:ident) => { ... };
    ($t:ident, $field:ident: $bit:expr) => { ... };
    ($t:ident, $field:ident { bit: $bit:expr, [$base:ty; $N:expr] }) => { ... };
}

Convenience macro for testing bitfields.