public void Clone()
        {
            var clonedClauseMapping = new QuerySourceMapping();
            var cloneContext        = new CloneContext(clonedClauseMapping);
            var clone = _resultOperator.Clone(cloneContext);

            Assert.That(clone, Is.InstanceOf(typeof(UnionResultOperator)));
            Assert.That(((UnionResultOperator)clone).ItemName, Is.EqualTo("itemName"));
            Assert.That(((UnionResultOperator)clone).Source2, Is.SameAs(_source2));
            Assert.That(((UnionResultOperator)clone).ItemType, Is.SameAs(typeof(int)));
        }