Cargo.toml

[package]
name = "foo"
version = "0.1.0"
edition = "2021"

# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html

[dependencies]

lib.rs

/// My `foo` macro!
///
/// ```compile_fail
/// # #[macro_use] extern crate foo;
/// # fn main() {
/// foo!();
/// # }
/// ```
#[macro_export]
macro_rules! foo {
    () => {
        // invalid syntax
        if {}
    }
}

$ cargo test --doc
    Finished test [unoptimized + debuginfo] target(s) in 0.00s
   Doc-tests foo

running 1 test
test src/lib.rs - foo (line 4) - compile fail ... ok

test result: ok. 1 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.01s