Call private methods of an object from a test assembly. (NUnit)

I have to test a class of Foo from my test assembly Foo.Test.
Unfortunately, many methods I should test are not public.

This class uses reflection to call private methods on any type or object for testing.

using System;
using System.Reflection;

namespace TestUtilities
{
    public class TestHelper
    {
        public static object InvokeStaticMethod(System.Type type, string methodName, object[] parameters)
        {
            BindingFlags bindFlags = BindingFlags.Static | BindingFlags.Public | BindingFlags.NonPublic;
            return InvokeMethod(type, methodName, null, parameters, bindFlags);
        }
        public static object InvokeInstanceMethod(System.Type type, object instance, string methodName, object[] parameters)
        {
            BindingFlags bindFlags = BindingFlags.Instance | BindingFlags.Public | BindingFlags.NonPublic;
            return InvokeMethod(type, methodName, instance, parameters, bindFlags);
        }
        private static object InvokeMethod(System.Type type, string methodName, object instance, object[] parameters, BindingFlags bindFlags)
        {
            MethodInfo methInfo;
            methInfo = type.GetMethod(methodName, bindFlags);
            if (methInfo == null)
            {
                throw new ArgumentException(String.Format("There is no method with name {0} on type {1}", methodName, type.Name));
            }

            object result = methInfo.Invoke(instance, parameters);
            return result;
        }

    }
}