Add test for subtraction overflow in DuplicatesBy

Author: arpankapoor

tests/test_std.rs

@@ -84,6 +84,13 @@ fn duplicates() {
     it::assert_equal(ys.iter(), xs.iter().rev().duplicates().rev());
     let ys_rev = [1, 0];
     it::assert_equal(ys_rev.iter(), xs.iter().duplicates().rev());
+
+    let xs = vec![0, 1, 2, 1, 2];
+    let ys = vec![1, 2];
+    assert_eq!(ys, xs.iter().duplicates().cloned().collect_vec());
+    assert_eq!(ys, xs.iter().rev().duplicates().rev().cloned().collect_vec());
+    let ys_rev = vec![2, 1];
+    assert_eq!(ys_rev, xs.iter().duplicates().rev().cloned().collect_vec());
 }
 
 #[test]