public void TestDic_Equality()
        {
            IEquatable <BiDictionary <int, string> > dic1 = new BiDictionary <int, string>()
            {
                { 1, "one" }
            };

            BiDictionary <int, string> dic2 = new BiDictionary <int, string>()
            {
                { 1, "one" }
            };

            Assert.True(dic1.Equals(dic2));
        }