public void FilterArrayByKey7()
        {
            var arr = new[] { 7, 1, 2, 3, 4, 5, 6, 7, 68, 69, 70, 15, 17 };

            CollectionAssert.AreEqual(new[] { 7, 7, 70, 17 }, ArrayExt.FilterArrayByKey(arr, 7));
        }