indexWriter.addDocument(doc()
.add(field("_id", "1")).build());
IndexReader reader = IndexReader.open(indexWriter, true);
assertThat(reader.numDocs(), equalTo(1));
indexWriter.prepareCommit();
reader = reader.reopen();
assertThat(reader.numDocs(), equalTo(1));
indexWriter.addDocument(doc()
.add(field("_id", "2")).build());