Testing memory usage when iterating IDictionary vs Dictionary

Program.cs

class Program
{
    const int trials = 1_000_000;

    static void Main(string[] args)
    {
        Dictionary<int, string> dict = Enumerable
            .Range(1, 10)
            .ToDictionary(number => number, number => number.ToString());

        var idict = (IDictionary<int, string>)dict;

        Console.ReadKey();

        // test iterating interface type
        GC.Collect();
        Test(idict);
        long idictMem = GC.GetTotalMemory(forceFullCollection: false);

        // test iterating concrete type
        GC.Collect();
        Test(dict);
        long dictMem = GC.GetTotalMemory(forceFullCollection: false);

        Console.WriteLine($"Dictionary: {dictMem} bytes, IDictionary: {idictMem} bytes, IDictionary uses {idictMem/dictMem}x more memory");
        // output on my machine: "Dictionary: 30616 bytes, IDictionary: 579480 bytes, IDictionary uses 18x more memory"
        Console.ReadKey();
    }

    private static void Test(Dictionary<int, string> dict)
    {
        for (int i = 0; i < trials; i++)
        {
            foreach (var kvp in dict)
            {
                // do something with key or values
            }
        }
    }

    private static void Test(IDictionary<int, string> dict)
    {
        for (int i = 0; i < trials; i++)
        {
            foreach (var kvp in dict)
            {
                // do something with key or values
            }
        }
    }
}