error: Documentation test in private item
  --> $DIR/private-item-doc-test.rs:14:5
   |
LL | /     /// private doc test
LL | |     ///
LL | |     /// ```
LL | |     /// assert!(false);
LL | |     /// ```
   | |___________^
   |
note: lint level defined here
  --> $DIR/private-item-doc-test.rs:11:9
   |
LL | #![deny(private_doc_tests)]
   |         ^^^^^^^^^^^^^^^^^