### Question:
TransactionIdTracker { public long newestEncounteredTxId() { return transactionIdStore().getLastCommittedTransactionId(); } TransactionIdTracker( Supplier<TransactionIdStore> transactionIdStoreSupplier, AvailabilityGuard databaseAvailabilityGuard ); void awaitUpToDate( long oldestAcceptableTxId, Duration timeout ); long newestEncounteredTxId();  }### Answer:
@Test public void shouldReturnNewestTransactionId() { when( transactionIdStore.getLastClosedTransactionId() ).thenReturn( 42L ); when( transactionIdStore.getLastCommittedTransactionId() ).thenReturn( 4242L ); assertEquals( 4242L, transactionIdTracker.newestEncounteredTxId() ); }