DO NOT MERGE: add test link

Author: RalfJung

library/core/src/primitive_docs.rs

@@ -942,6 +942,8 @@ mod prim_slice {}
 /// Note: This example shows the internals of `&str`. `unsafe` should not be
 /// used to get a string slice under normal circumstances. Use `as_str`
 /// instead.
+///
+/// [THIS IS A TEST](../std/process/fn.exit.html).
 #[stable(feature = "rust1", since = "1.0.0")]
 mod prim_str {}