Fix ignored doctest of size_hint::mul

This doctest can not run because this function (and module) is private.

Author: Philippe-Cholet

src/size_hint.rs

@@ -38,20 +38,6 @@ pub fn sub_scalar(sh: SizeHint, x: usize) -> SizeHint {
 }
 
 /// Multiply `SizeHint` correctly
-///
-/// ```ignore
-/// use std::usize;
-/// use itertools::size_hint;
-///
-/// assert_eq!(size_hint::mul((3, Some(4)), (3, Some(4))),
-///            (9, Some(16)));
-///
-/// assert_eq!(size_hint::mul((3, Some(4)), (usize::MAX, None)),
-///            (usize::MAX, None));
-///
-/// assert_eq!(size_hint::mul((3, None), (0, Some(0))),
-///            (0, Some(0)));
-/// ```
 #[inline]
 pub fn mul(a: SizeHint, b: SizeHint) -> SizeHint {
     let low = a.0.saturating_mul(b.0);
@@ -100,3 +86,10 @@ pub fn min(a: SizeHint, b: SizeHint) -> SizeHint {
     };
     (lower, upper)
 }
+
+#[test]
+fn mul_size_hints() {
+    assert_eq!(mul((3, Some(4)), (3, Some(4))), (9, Some(16)));
+    assert_eq!(mul((3, Some(4)), (usize::MAX, None)), (usize::MAX, None));
+    assert_eq!(mul((3, None), (0, Some(0))), (0, Some(0)));
+}