from unittest.mock import AsyncMock, MagicMock

import pytest


@pytest.fixture
def reader_double():
    """Factory of OPC reader doubles holding subscriptions for the given slots.

    Like the real ServerReader, `subscriptions` is keyed by slot
    and `unsubscribe` drops the slot from it.
    """

    def make(*slots):
        reader = MagicMock()
        reader.subscriptions = {slot: MagicMock() for slot in slots}
        reader.unsubscribe = AsyncMock(side_effect=lambda slot: reader.subscriptions.pop(slot))
        return reader

    return make