public void CommonEnd()
        {
            var test1 = new string[] { };
            Assert.AreEqual("", test1.CommonEnd());

            var test2 = new[] { "12" };
            Assert.AreEqual("12", test2.CommonEnd());

            var test3 = new[] { "", "", "" };
            Assert.AreEqual("", test3.CommonEnd());

            var test4 = new[] { "", "12", "" };
            Assert.AreEqual("", test4.CommonEnd());

            var test5 = new[] { "12", "12", "123" };
            Assert.AreEqual("", test5.CommonEnd());

            var test6 = new[] { "012", "012", "312" };
            Assert.AreEqual("12", test6.CommonEnd());
        }