Example of Cargo- and rustdoc-built tests failing for tests derived from macro doc-comments

Cargo.toml

[package]
name="bob"
version="0.0.1"
authors=["insaneinside"]

[lib]
name="bob"
path="lib.rs"

lib.rs

/// Panic with a given message unless an expression evaluates to true.
///
/// ## Examples
/// ```rust
/// panic_unless!(1 + 1 == 2, "Math is broken.");
/// ```
///
/// ```rust,should_fail
/// panic_unless!(true == false, "I'm broken.");
/// ```
#[macro_export]
macro_rules! panic_unless {
    ($condition:expr, $($rest:expr),+) => ({ if ! $condition { panic!($($rest),+); } });
}