public virtual void TestClone()
{
var q = new DrillDownQuery(config, new MatchAllDocsQuery());
q.Add("a");
var clone = q.Clone() as DrillDownQuery;
Assert.NotNull(clone);
clone.Add("b");
Assert.False(q.ToString().Equals(clone.ToString(), StringComparison.Ordinal), "query wasn't cloned: source=" + q + " clone=" + clone);
}