def METHOD_NAME(instance: DagsterInstance, external_repo: ExternalRepository):
    external_partition_set = external_repo.get_external_partition_set("the_job_partition_set")
    instance.add_backfill(
        PartitionBackfill(
            backfill_id="simple",
            partition_set_origin=external_partition_set.get_external_origin(),
            status=BulkActionStatus.REQUESTED,
            partition_names=["one", "two", "three"],
            from_failure=False,
            reexecution_steps=None,
            tags=None,
            backfill_timestamp=pendulum.now().timestamp(),
        )
    )
    launch_process = spawn_ctx.Process(
        target=_test_backfill_in_subprocess,
        args=[instance.get_ref(), None],
    )
    launch_process.start()
    launch_process.join(timeout=60)
    backfill = instance.get_backfill("simple")
    assert backfill
    assert backfill.status == BulkActionStatus.COMPLETED