public virtual void  TestCaching()
        {
            Directory   dir    = new RAMDirectory();
            IndexWriter writer = new IndexWriter(dir, new SimpleAnalyzer(), IndexWriter.MaxFieldLength.LIMITED);
            Document    doc    = new Document();
            TokenStream stream = new AnonymousClassTokenStream(this);

            stream = new CachingTokenFilter(stream);

            doc.Add(new Field("preanalyzed", stream, TermVector.NO));

            // 1) we consume all tokens twice before we add the doc to the index
            checkTokens(stream);
            stream.Reset();
            checkTokens(stream);

            // 2) now add the document to the index and verify if all tokens are indexed
            //    don't reset the stream here, the DocumentWriter should do that implicitly
            writer.AddDocument(doc);
            writer.Close();

            IndexReader   reader        = IndexReader.Open(dir);
            TermPositions termPositions = reader.TermPositions(new Term("preanalyzed", "term1"));

            Assert.IsTrue(termPositions.Next());
            Assert.AreEqual(1, termPositions.Freq());
            Assert.AreEqual(0, termPositions.NextPosition());

            termPositions.Seek(new Term("preanalyzed", "term2"));
            Assert.IsTrue(termPositions.Next());
            Assert.AreEqual(2, termPositions.Freq());
            Assert.AreEqual(1, termPositions.NextPosition());
            Assert.AreEqual(3, termPositions.NextPosition());

            termPositions.Seek(new Term("preanalyzed", "term3"));
            Assert.IsTrue(termPositions.Next());
            Assert.AreEqual(1, termPositions.Freq());
            Assert.AreEqual(2, termPositions.NextPosition());
            reader.Close();

            // 3) reset stream and consume tokens again
            stream.Reset();
            checkTokens(stream);
        }