At long list I have published version 0.5.0 of rust-skeptic, the tool for testing Markdown files via Cargo. Skeptic is similar to rustdoc --test
but has a slightly more principled design and integrates with Cargo to test single mardown files.
0.5.0
Thanks to skeptic contributors: Brian Anderson, Christopher Brickley, Johann Hofmann, Paul Osborne, Ryman
You may also be interested in @pnkfelix's tango, a similar but different tool.