     end
   end
 
-  @tag :pending
   describe "add" do
+    @tag :pending
     test "add to empty set" do
       custom_set = CustomSet.new([])
       actual = CustomSet.add(custom_set, 3)

      assert CustomSet.equal?(actual, expected)
    end

    test "adding an existing element does not change the set" do
      expected = CustomSet.new([1, 2, 3])
      actual = CustomSet.add(expected, 3)

      assert CustomSet.equal?(actual, expected)
    end

    @tag :pending
    test "union of an empty set and non-empty set is the non-empty set" do
      custom_set_1 = CustomSet.new([])
      custom_set_2 = CustomSet.new([2])
