i am unable to make the smart unit test in visual studio 2015? [duplicate]

This question already has an answer here:

• Default visibility for C# classes and members (fields, methods, etc)? 3 answers

this is my code.

class Program
{
    public static void cal(int n1, int n2,
         out int add, out int sub, out int mul, out float div)
    {
        add = n1 + n2;
        sub = n1 - n2;
        mul = n1 * n2;
        div = (float)n1 / n2;
    }
    static void Main(string[] args)
    {
        int n1, n2;
        int add, sub, mul;
        float div;
        Console.Write("Enter 1st number");
        n1 = Convert.ToInt32(Console.ReadLine());
        Console.Write("\nEnter 2nd number");
        n2 = Convert.ToInt32(Console.ReadLine());

        Program.cal(n1, n2, out add, out sub, out mul, out div);
        Console.WriteLine("\n\n{0} + {1} = {2}", n1, n2, add);
        Console.WriteLine("{0} - {1} = {2}", n1, n2, sub);
        Console.WriteLine("{0} * {1} = {2}", n1, n2, mul);
        Console.WriteLine("{0} / {1} = {2}", n1, n2, div);

        Console.ReadLine();
    }

}

when i goes on method or class and perform right click on it and make a smart unit test then it show an error like- the selected type is not visible and can not be explored/ can not run the test for selected type bcoz the type is not visible. please help me to short out this problem.