57 lines
2.1 KiB
Python
57 lines
2.1 KiB
Python
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"""Verify the Settings → Rates fixed-mode arithmetic.
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For 100% stocks with growth=6% and dividend=2.5%, inflation=3%, the
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expected real return per year is ``(1 + 0.06 + 0.025) / 1.03 - 1``
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≈ 0.0534. We assert the simulator's portfolio compounds at this rate
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in the absence of withdrawals (spending=0, no strategy draw).
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"""
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from __future__ import annotations
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from decimal import Decimal
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import numpy as np
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import pytest
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from fire_planner.api.schemas import SimulateRequest
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from fire_planner.api.simulate import _build_paths, _project
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@pytest.mark.asyncio
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async def test_fixed_rates_real_return_arithmetic() -> None:
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req = SimulateRequest(
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jurisdiction="uae", # 0% tax to isolate compounding
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strategy="trinity",
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leave_uk_year=0,
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spending_gbp=Decimal("1"),
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nw_seed_gbp=Decimal("100000"),
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horizon_years=30,
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n_paths=100,
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rates_mode="fixed",
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inflation_pct=Decimal("0.03"),
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stocks_growth_pct=Decimal("0.06"),
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stocks_dividend_pct=Decimal("0.025"),
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bonds_growth_pct=Decimal("0.015"),
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bonds_dividend_pct=Decimal("0.035"),
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stocks_allocation=Decimal("1"),
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)
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paths = await _build_paths(req)
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assert paths.shape == (100, 30, 3)
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# nominal stock return embedded should be growth + dividend = 0.085
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assert paths[0, 0, 0] == pytest.approx(0.085)
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assert paths[0, 0, 1] == pytest.approx(0.05)
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assert paths[0, 0, 2] == pytest.approx(0.03)
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expected_real = (1 + 0.06 + 0.025) / (1 + 0.03) - 1
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assert expected_real == pytest.approx(0.0534, abs=1e-3)
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result, _ = _project(req, paths)
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# All paths identical → median == any single path. After 30 years of
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# compounding 0.0534 with the trinity 4% draw, ending NW lies in a
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# well-defined window.
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end_real = float(np.median(result.portfolio_real[:, -1]))
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assert end_real > 100_000 # grew despite the £1/y withdrawal
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growth_factor = end_real / 100_000.0
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expected_factor = (1 + expected_real)**30
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# Loose because trinity strategy still draws something each year.
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assert growth_factor == pytest.approx(expected_factor, rel=0.05)
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