Test that the following scenario will hit prepare conflicts:

1. Create a collection and add a unique index on the 'a' field
2. Start a transaction
3. Insert {_id: 1, a: 1}
4. Update that unsets 'a' for {_id: 1}
5. Prepare the transaction
6. Outside of a transaction try to insert {_id: 2, a: 1}

If this scenario did not encounter a prepare conflict, it would cause issues when recover prepared transactions at the end of initial sync. The initial insert in the transaction would fail with a duplicate key error and its update would also fail.