std: move "mod tests/benches" to separate files

Also doing fmt inplace as requested.

library/std/src/io/util.rs

@@ -1,5 +1,8 @@
 #![allow(missing_copy_implementations)]
 
+#[cfg(test)]
+mod tests;
+
 use crate::fmt;
 use crate::io::{self, BufRead, ErrorKind, Initializer, IoSlice, IoSliceMut, Read, Write};
 use crate::mem::MaybeUninit;
@@ -254,52 +257,3 @@ impl fmt::Debug for Sink {
         f.pad("Sink { .. }")
     }
 }
-
-#[cfg(test)]
-mod tests {
-    use crate::io::prelude::*;
-    use crate::io::{copy, empty, repeat, sink};
-
-    #[test]
-    fn copy_copies() {
-        let mut r = repeat(0).take(4);
-        let mut w = sink();
-        assert_eq!(copy(&mut r, &mut w).unwrap(), 4);
-
-        let mut r = repeat(0).take(1 << 17);
-        assert_eq!(copy(&mut r as &mut dyn Read, &mut w as &mut dyn Write).unwrap(), 1 << 17);
-    }
-
-    #[test]
-    fn sink_sinks() {
-        let mut s = sink();
-        assert_eq!(s.write(&[]).unwrap(), 0);
-        assert_eq!(s.write(&[0]).unwrap(), 1);
-        assert_eq!(s.write(&[0; 1024]).unwrap(), 1024);
-        assert_eq!(s.by_ref().write(&[0; 1024]).unwrap(), 1024);
-    }
-
-    #[test]
-    fn empty_reads() {
-        let mut e = empty();
-        assert_eq!(e.read(&mut []).unwrap(), 0);
-        assert_eq!(e.read(&mut [0]).unwrap(), 0);
-        assert_eq!(e.read(&mut [0; 1024]).unwrap(), 0);
-        assert_eq!(e.by_ref().read(&mut [0; 1024]).unwrap(), 0);
-    }
-
-    #[test]
-    fn repeat_repeats() {
-        let mut r = repeat(4);
-        let mut b = [0; 1024];
-        assert_eq!(r.read(&mut b).unwrap(), 1024);
-        assert!(b.iter().all(|b| *b == 4));
-    }
-
-    #[test]
-    fn take_some_bytes() {
-        assert_eq!(repeat(4).take(100).bytes().count(), 100);
-        assert_eq!(repeat(4).take(100).bytes().next().unwrap().unwrap(), 4);
-        assert_eq!(repeat(1).take(10).chain(repeat(2).take(10)).bytes().count(), 20);
-    }
-}