APINonTxTest is leaking transactions in testReplaceNullKeyParameter() and related methods (for transaction configurations). The implicit transaction is created and then a NullPointerException is thrown because of invalid arguments. The transaction stays in TransactionTable forever making the TransactionTable.stop() slow.
testStopClearsData() runs slow (30sec) because it waits for the leaking transactions to finish (in a total of 2 min since the test is executed 4 times for different tx configurations)

IMO, the best solution would be a Supplier or IntFunction and only create the InvocationContext and implicit transaction in the last moment.