custom-set: sync (exercism#1923)

exercises/practice/custom-set/.meta/tests.toml

@@ -114,6 +114,9 @@ description = "Difference (or Complement) of a set is a set of all elements that
 [c5ac673e-d707-4db5-8d69-7082c3a5437e]
 description = "Difference (or Complement) of a set is a set of all elements that are only in the first set -> difference of two non-empty sets is a set of elements that are only in the first set"
 
+[20d0a38f-7bb7-4c4a-ac15-90c7392ecf2b]
+description = "Difference (or Complement) of a set is a set of all elements that are only in the first set -> difference removes all duplicates in the first set"
+
 [c45aed16-5494-455a-9033-5d4c93589dc6]
 description = "Union returns a set of all elements in either set -> union of empty sets is an empty set"
 

exercises/practice/custom-set/tests/custom-set.rs

@@ -286,6 +286,15 @@ fn difference_of_two_non_empty_sets_is_a_set_of_elements_that_are_only_in_the_fi
     assert_eq!(set_1.difference(&set_2), expected);
 }
 
+#[test]
+#[ignore]
+fn difference_removes_all_duplicates_in_the_first_set() {
+    let set_1 = CustomSet::<i32>::new(&[1, 1]);
+    let set_2 = CustomSet::<i32>::new(&[1]);
+    let expected = CustomSet::<i32>::new(&[]);
+    assert_eq!(set_1.difference(&set_2), expected);
+}
+
 #[test]
 #[ignore]
 fn union_of_empty_sets_is_an_empty_set() {