There are already a few test's that start a transaction explicitly:

In dbapi.SqliteOnConflictTests CheckOnConflictRollbackWithExplicitTransaction, CheckOnConflictAbortRaisesWithExplicitTransactions which set ``isolation_level = None``.

On the other hand in transaction.TransactionalDDL.CheckTransactionalDDL the test do not set the isolation_level to None but start a transaction explicitly. The test pass because sqlite3_stmt_readonly return true for "begin" and "begin deferred".

I think that if we say that in order to start a transaction implicitly the isolation_level needs to be None CheckTransactionalDDL should be changed.