Macro expect_empty

macro_rules! expect_empty {
    ( $a:expr ) => { ... };
}

Expects that the given container (e.g., Vec) is empty; otherwise returns early.

Examples

fn passing_test() -> Result<()> {
    let empty: Vec<i32> = vec![];
    expect_empty!(empty);
    Ok(())
}

fn failing_test() -> Result<()> {
    expect_empty!(vec![0, 1, 1, 2, 3, 5, 8, 13, 21]);  // returns early
    Ok(())  // won't be reached
}