✅ Black serpent upkeep at main phase start

Category	Ability
Status	Passing
Test	tests/test_abilities_familiars.py::test_black_serpent_upkeep_at_main_phase_start

Black Serpent takes 2 Fixed Damage at start of owner's main phase.

Preconditions

• Lane 0: P1's Black Serpent (098_1) — READIED, 0 damage.

Action

• Fire MAIN_PHASE_START event for P1.

new_state = fire_event(
        state,
        GameEvent(
            event_type=EventType.MAIN_PHASE_START,
            source=None,
            target=None,
            value=None,
            side=Side.PLAYER_1,
            lane=None,
        ),
    )

    serpent_after = next(d for d in new_state.demons if d.unit_id == "098_1")

Expected Postconditions

• Black Serpent damage = 2.

Assertions

assert serpent_after.damage == 2, (
        f"Black Serpent should have 2 damage from upkeep, got {serpent_after.damage}"
    )