Macro debug_assert_ready_err 

macro_rules! debug_assert_ready_err {
    ($($arg:tt)*) => { ... };
}

Asserts that expression returns Poll::Ready(Err(E)) variant in runtime.

Like assert_ready_err!, this macro also has a second version, where a custom panic message can be provided.

Uses

See debug_assert! documentation for possible use cases. The same applies to this macro.