Today I've published a tiny crate doubter, which helps testing code blocks in Markdown files.
The approach adopted by doubter is to embed Markdown files as doc-comments into Rust source code. It is corresponding to the unstable attribute #[doc(include = "...")], but doubter makes it possible to use it on the stable compiler by emulating it as a procedural macro.
Currently, the crate is the experimental stage and I'm looking for feedback from many users. If you are interested, let's try it and send issue or PR.
It assumes that the crate for testing Markdowns with doubter is not subject to publication and separated with the crate to be tested (so the testing crate is often managed in workspace). As a result, doc comments generated by doubter will not be appear in the published crate.