def METHOD_NAME(self):
    data_source = DataSource.lookup(self._db, DataSource.GUTENBERG)
    id = "549"
    # We've got a record.
    record, was_new = Edition.for_foreign_id(
        self._db, data_source, Identifier.GUTENBERG_ID, id)
    # Then we look it up and discover another identifier for it.
    data_source_2 = DataSource.lookup(self._db, DataSource.OCLC)
    record2, was_new = Edition.for_foreign_id(
        self._db, data_source_2, Identifier.OCLC_NUMBER, "22")
    eq = record.primary_identifier.equivalent_to(
        data_source_2, record2.primary_identifier, 1)
    assert eq.input == record.primary_identifier
    assert eq.output == record2.primary_identifier
    assert eq.data_source == data_source_2
    assert [eq] == record.primary_identifier.equivalencies
    assert set([record, record2]) == set(record.equivalent_editions().all())