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());
}