diff --git a/src/tests/adding.md b/src/tests/adding.md
index ebbbb1cfc..10483265c 100644
--- a/src/tests/adding.md
+++ b/src/tests/adding.md
@@ -17,8 +17,11 @@ guidelines:
   - The majority of standard library tests are written as doctests, which
     illustrate and exercise typical API behavior.
   - Additional [unit tests](intro.md#package-tests) should go in
-    `library/${crate}/tests` (where `${crate}` is usually `core`, `alloc`, or
-    `std`).
+    `library/${crate}/tests` (where `${crate}` is usually `std`).
+  - Tests for the `alloc` or `core` crates must go in separate crates: `alloctests` or `coretests` respectively.
+    - NOTE: That when adding unit tests for unstable features the `#![feature(...)]`
+      declaration must be added to `library/${crate}tests/tests/lib.rs` and not to
+      `library/${crate}tests/lib.rs`.
 - If the code is part of an isolated system, and you are not testing compiler
   output, consider using a [unit or integration test](intro.md#package-tests).
 - Need to run rustdoc? Prefer a `rustdoc` or `rustdoc-ui` test. Occasionally