Doc comments are very useful for big projects that require documentation. When running Rustdoc, these are the comments that get compiled into documentation. They are denoted by a ///, and support Markdown.

XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX

To run the tests, first build the code as a library, then tell rustdoc where to find the library so it can link it into each doctest program:

$ rustc doc.rs --crate-type lib
$ rustdoc --test --extern doc="libdoc.rlib" doc.rs

(When you run cargo test on a library crate, Cargo will automatically generate and run the correct rustc and rustdoc commands.)