public void GetHashCode_NotZero_ReturnsTrue()
        {
            var comparer = new BothNullOrNotNullComparer();
            var hasCode  = comparer.GetHashCode(new object());

            Assert.NotEqual(0, hasCode);
        }
        public void GetHashCode_Null_Throws()
        {
            var comparer = new BothNullOrNotNullComparer();

            Assert.Throws <ArgumentNullException>(() => comparer.GetHashCode(null));
        }