For the assertSessionTransactionState operation in transaction spec tests the session's internal state must be exposed, which is not currently exposed. Instead, the MongoDB\Driver\Session::isInTransaction method exposes a boolean to indicate whether a session is currently in progress (as denoted by the in_progress and starting states. To cover all cases of the test operation, it may be necessary to expose the internal transaction state to the outside world.

Note that this requires upstream changes in libmongoc as the internal state is not exposed there either.