public void CommonStart() { var test1 = new string[] {}; Assert.AreEqual("", test1.CommonStart()); var test2 = new[] { "12" }; Assert.AreEqual("12", test2.CommonStart()); var test3 = new[] { "", "", "" }; Assert.AreEqual("", test3.CommonStart()); var test4 = new[] { "", "12", "" }; Assert.AreEqual("", test4.CommonStart()); var test5 = new[] { "12", "12", "123" }; Assert.AreEqual("12", test5.CommonStart()); }