feat(CORE-002): add GLD share quote conversion seam

tests/test_instruments.py

@@ -0,0 +1,52 @@
+from __future__ import annotations
+
+from decimal import Decimal
+
+import pytest
+
+from app.domain.backtesting_math import AssetQuantity, PricePerAsset
+from app.domain.instruments import (
+    asset_quantity_from_weight,
+    price_per_weight_from_asset_price,
+    weight_from_asset_quantity,
+)
+from app.domain.units import BaseCurrency, Weight, WeightUnit
+
+
+def test_gld_share_quantity_converts_to_troy_ounce_weight() -> None:
+    quantity = AssetQuantity(amount=Decimal("10"), symbol="GLD")
+
+    weight = weight_from_asset_quantity(quantity)
+
+    assert weight == Weight(amount=Decimal("1.0"), unit=WeightUnit.OUNCE_TROY)
+
+
+def test_gld_troy_ounce_weight_converts_to_share_quantity() -> None:
+    weight = Weight(amount=Decimal("1"), unit=WeightUnit.OUNCE_TROY)
+
+    quantity = asset_quantity_from_weight("GLD", weight)
+
+    assert quantity == AssetQuantity(amount=Decimal("10"), symbol="GLD")
+
+
+def test_gld_share_quote_converts_to_ounce_equivalent_spot() -> None:
+    quote = PricePerAsset(amount=Decimal("404.19"), currency=BaseCurrency.USD, symbol="GLD")
+
+    spot = price_per_weight_from_asset_price(quote, per_unit=WeightUnit.OUNCE_TROY)
+
+    assert spot.amount == Decimal("4041.9")
+    assert spot.currency is BaseCurrency.USD
+    assert spot.per_unit is WeightUnit.OUNCE_TROY
+
+
+def test_instrument_conversions_fail_closed_for_unsupported_symbols() -> None:
+    quote = PricePerAsset(amount=Decimal("28.50"), currency=BaseCurrency.USD, symbol="SLV")
+
+    with pytest.raises(ValueError, match="Unsupported instrument metadata"):
+        price_per_weight_from_asset_price(quote, per_unit=WeightUnit.OUNCE_TROY)
+
+    with pytest.raises(ValueError, match="Unsupported instrument metadata"):
+        weight_from_asset_quantity(AssetQuantity(amount=Decimal("10"), symbol="SLV"))
+
+    with pytest.raises(ValueError, match="Unsupported instrument metadata"):
+        asset_quantity_from_weight("SLV", Weight(amount=Decimal("1"), unit=WeightUnit.OUNCE_TROY))