I may not be following your point, but I don't believe the root cause of this issue was a race condition, or anything that might be related to concurrency.
The fundamental cause AFAIK was a SQLite connection was attempting to make a state transition (from one type of locking state to another) which shouldn't be allowed under certain circumstances, but the implementation didn't actually enforce this rule. So the added test really does test the root cause.
The fundamental cause AFAIK was a SQLite connection was attempting to make a state transition (from one type of locking state to another) which shouldn't be allowed under certain circumstances, but the implementation didn't actually enforce this rule. So the added test really does test the root cause.