Rollup merge of #52769 - sinkuu:stray_test, r=alexcrichton

Incorporate a stray test

`liballoc/repeat-generic-slice.rs` doesn't seem to be tested (I think it was intended to be placed in `run-pass`). This PR incorporates the test into `liballoc/tests`.

diff --combined src/liballoc/tests/lib.rs
index 91bc778ad4c1ec6b3cb5f6778689e6b748a8e301,d3cbad0284b464068decd8599b5c5df437347a2a..618aff963f22dd59bc8d549bd4fc585ecd4d8847
--- 1/src/liballoc/tests/lib.rs
--- 2/src/liballoc/tests/lib.rs
+++ b/src/liballoc/tests/lib.rs
@@@ -24,6 -24,7 +24,7 @@@
  #![feature(try_reserve)]
  #![feature(unboxed_closures)]
  #![feature(exact_chunks)]
+ #![feature(repeat_generic_slice)]
  
  extern crate alloc_system;
  extern crate core;
@@@ -63,7 -64,7 +64,7 @@@ fn test_boxed_hasher() 
      5u32.hash(&mut hasher_1);
      assert_eq!(ordinary_hash, hasher_1.finish());
  
 -    let mut hasher_2 = Box::new(DefaultHasher::new()) as Box<Hasher>;
 +    let mut hasher_2 = Box::new(DefaultHasher::new()) as Box<dyn Hasher>;
      5u32.hash(&mut hasher_2);
      assert_eq!(ordinary_hash, hasher_2.finish());
  }