Write a C# Sharp program to check if a given string contains only lowercase or uppercase characters

using System;
using System.Linq;
namespace exercises
{
    class Program
    {
        static void Main(string[] args)
        {
            Console.WriteLine(test("PHP"));
            Console.WriteLine(test("python"));
            Console.WriteLine(test("JavaScript"));
        }
        public static bool test(string str1)
        {
            return str1 == str1.ToUpper() | str1 == str1.ToLower();
        }
    }
}