Restore commented tests (#665)

These seem to have been commented by accident in #298, and are still
passing.

src/bytes_mut.rs

@@ -1409,9 +1409,12 @@ fn original_capacity_from_repr(repr: usize) -> usize {
     1 << (repr + (MIN_ORIGINAL_CAPACITY_WIDTH - 1))
 }
 
-/*
+#[cfg(test)]
-#[test]
+mod tests {
-fn test_original_capacity_to_repr() {
+    use super::*;
+
+    #[test]
+    fn test_original_capacity_to_repr() {
         assert_eq!(original_capacity_to_repr(0), 0);
 
         let max_width = 32;
@@ -1442,10 +1445,10 @@ fn test_original_capacity_to_repr() {
                 assert_eq!(original_capacity_to_repr(cap - 48), expected - 1);
             }
         }
-}
+    }
 
-#[test]
+    #[test]
-fn test_original_capacity_from_repr() {
+    fn test_original_capacity_from_repr() {
         assert_eq!(0, original_capacity_from_repr(0));
 
         let min_cap = 1 << MIN_ORIGINAL_CAPACITY_WIDTH;
@@ -1457,8 +1460,8 @@ fn test_original_capacity_from_repr() {
         assert_eq!(min_cap * 16, original_capacity_from_repr(5));
         assert_eq!(min_cap * 32, original_capacity_from_repr(6));
         assert_eq!(min_cap * 64, original_capacity_from_repr(7));
+    }
 }
-*/
 
 unsafe impl Send for BytesMut {}
 unsafe impl Sync for BytesMut {}