public void IndexOf(
            [Values(10, 20, 30, 100, 40)] int value,
            [Values(0, 1, 3, 6, -1)] int expectedIndex)
        {
            int index = set.IndexOf(value);

            Assert.AreEqual(expectedIndex, index);
        }
        private void MultiSetIndexOf()
        {
            int index;

            for (int i = 0; i < count; i++)
            {
                index = multiSet.IndexOf(data[i]);
            }
        }