from reactor_sim.neutronics import NeutronDynamics
from reactor_sim.state import CoreState


def _core_state(
    temperature: float = 950.0,
    flux: float = 2e7,
    burnup: float = 0.01,
    power: float = 500.0,
) -> CoreState:
    return CoreState(
        fuel_temperature=temperature,
        neutron_flux=flux,
        reactivity_margin=0.0,
        power_output_mw=power,
        burnup=burnup,
    )


def test_reactivity_increases_with_rod_withdrawal():
    dynamics = NeutronDynamics()
    state = _core_state()
    rho_full_out = dynamics.reactivity(state, control_fraction=0.0)
    rho_half = dynamics.reactivity(state, control_fraction=0.5)
    assert rho_full_out > 0.0
    assert rho_full_out > rho_half