Function doc_test_set 

pub fn doc_test_set<'a>(
    docs: impl IntoIterator<Item = (&'a str, &'a Doc)>,
) -> Result<Vec<Generated>, String>

Every doc-test file a package needs: one module per page with testable blocks under DOC_TESTS_DIR, and the main.rs that declares them. Empty when no page has a testable block. An error names two pages whose paths sanitize to the same module.