Macro expect 

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

Expects that the given condition evaluates to true; otherwise returns early.

Examples

fn passing_test() -> Result<()> {
    expect!(1 + 1 == 2);
    Ok(())
}

fn failing_test() -> Result<()> {
    expect!(1 + 1 == 69);  // returns early
    Ok(())  // won't be reached
}

failing_test() will return early after calling expect!. The Err will be wrapped in a descriptive error message such as:

[my/file.rs:12] “expect!(condition)” Expected true but was false.
[ … wrapped Err details …]