"""Unit tests for Sheet 2: Commercial Bank (Part II — 2.2)."""

import pytest
from fqbm.state import FQBMState
from fqbm.sheets.commercial_bank import (
    commercial_bank_step,
    CommercialBankParams,
    loans_max,
    capital_ratio,
)


def test_loan_deposit_identity():
    """dLoans = dDeposits."""
    state = FQBMState(Loans=900, Deposits=1000, E_b=100)
    params = CommercialBankParams(d_deposits=50)
    out = commercial_bank_step(state, params)
    assert out.Loans == 950
    assert out.Deposits == 1050


def test_loans_max():
    """Loans_max = Equity / k."""
    assert loans_max(100, 0.08) == pytest.approx(1250)
    assert loans_max(100, 0.10) == 1000


def test_capital_ratio():
    """CR = Equity / RWA."""
    assert capital_ratio(100, 1000) == 0.1
    assert capital_ratio(80, 1000) == 0.08