Summary

Add automated test fixtures for DBRef encoding and decoding behaviors described in the prose test plan in dbref.md.

Motivation

Who is the affected end user?

Drivers that provide a DBRef model class.

How does this affect the end user?

Currently there are no machine-readable test fixtures to validate DBRef behavior across drivers, only prose tests that each driver must interpret independently.

How likely is it that this problem or use case will occur?

Any driver implementing DBRef model support.

If the problem does occur, what are the consequences and how severe are they?

Inconsistent DBRef behavior across drivers.

Is this issue urgent?

No.

Is this ticket required by a downstream team?

No.

Is this ticket only for tests?

Yes.

Acceptance Criteria

Each driver that provides a DBRef model class implements the test fixtures proposed in the spec PR (to be linked). Behaviors covered: decoding valid/invalid documents, out-of-order field handling, encoding canonical field order, extra field support.