def METHOD_NAME(self):
    """Test attachment behaviour for only unknown formats."""
    x_pres_proposal = V20PresProposal(
        comment="Test",
        formats=[V20PresFormat(attach_id="not_indy", format_="not_indy")],
        proposals_attach=[
            AttachDecorator.data_base64(ident="not_indy", mapping=INDY_PROOF_REQ[0])
        ],
    )
    assert x_pres_proposal.attachment() is None