43 lines
1021 B
Python
43 lines
1021 B
Python
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"""Tests for Sheet 4: FX parity (Part III–IV)."""
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import pytest
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from fqbm.state import FQBMState
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from fqbm.sheets.fx_parity import (
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covered_interest_parity_fwd,
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uncovered_interest_parity_ds,
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dornbusch_s,
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fx_pass_through_inflation,
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fx_parity_step,
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FXParams,
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)
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def test_cip():
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F = covered_interest_parity_fwd(1.0, 0.05, 0.03)
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assert F > 1.0
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assert abs(F - 1.0 * (1.05 / 1.03)) < 1e-6
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def test_uip():
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ds = uncovered_interest_parity_ds(1.0, 0.05, 0.03)
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assert abs(ds - 0.02) < 1e-6
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def test_dornbusch():
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s = dornbusch_s(1.0, 0.05, 0.03, 1.5)
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assert s > 1.0
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assert abs(s - 1.0 - 1.5 * 0.02) < 1e-6
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def test_fx_pass_through():
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pi = fx_pass_through_inflation(0.1, 0.2)
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assert pi == pytest.approx(0.02)
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def test_fx_parity_step():
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state = FQBMState(S=1.0)
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params = FXParams(s_star=1.0, i_d=0.05, i_f=0.03, lambda_dornbusch=2.0)
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out = fx_parity_step(state, params)
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assert out.S != 1.0
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assert out.S == pytest.approx(1.0 + 2.0 * 0.02)
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