From our discussion with Sanne:

• The transaction timeout in tests should be low (2000ms), so that we trigger timeouts
• Ideally, the mass indexer should "ping" the transaction manager regularly to postpone the timeout as long as the mass indexer is still
• currently, the old mass indexer uses org.hibernate.search.batchindexing.impl.OptionallyWrapInJTATransaction to open very long transactions