From 0220bee87cfab0c2319c2b94c71786b347505af8 Mon Sep 17 00:00:00 2001
From: Khalim Conn-Kowlessar <kconnkowlessar@gmail.com>
Date: Thu, 9 Jul 2026 11:41:27 +0000
Subject: [PATCH] =?UTF-8?q?Forced=20ventilation=20is=20injected=20once=20a?=
 =?UTF-8?q?cross=20both=20fabric-first=20phases=20=F0=9F=9F=A5?=
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Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
---
 .../modelling/test_optimiser_fabric_first.py  | 100 ++++++++++++++++++
 1 file changed, 100 insertions(+)

diff --git a/tests/domain/modelling/test_optimiser_fabric_first.py b/tests/domain/modelling/test_optimiser_fabric_first.py
index 0fd088627..71ce7a4f6 100644
--- a/tests/domain/modelling/test_optimiser_fabric_first.py
+++ b/tests/domain/modelling/test_optimiser_fabric_first.py
@@ -18,6 +18,7 @@ from datatypes.epc.domain.epc_property_data import (
 )
 from domain.modelling.measure_type import MeasureType
 from domain.modelling.optimisation.optimiser import (
+    MeasureDependency,
     OptimisedPackage,
     ScoredOption,
     optimise_package_fabric_first,
@@ -29,6 +30,7 @@ from domain.modelling.simulation import (
     EpcSimulation,
     GlazingOverlay,
     HeatingOverlay,
+    VentilationOverlay,
 )
 from tests.domain.sap10_calculator.worksheet._elmhurst_worksheet_000490 import (
     build_epc,
@@ -175,6 +177,104 @@ def test_fabric_spend_comes_out_of_the_shared_budget_before_phase_two() -> None:
     assert abs(package.score.sap_continuous - 65.0) <= 1e-9
 
 
+_IWI_OVERLAY = EpcSimulation(
+    building_parts={
+        BuildingPartIdentifier.MAIN: BuildingPartOverlay(wall_insulation_type=3)
+    }
+)
+_VENT_OVERLAY = EpcSimulation(
+    ventilation=VentilationOverlay(mechanical_ventilation_kind="EXTRACT_OR_PIV_OUTSIDE")
+)
+
+
+class _TwoWallScorer:
+    """A stub with two wall treatments (cavity type=2, internal type=3): the
+    internal wall is worthless raw but +4 once the cavity is done, and every
+    ventilation overlay present costs −1 — so both phases trigger the same
+    forced ventilation dependency and a double injection is visible in the
+    package score."""
+
+    def score(
+        self, baseline: EpcPropertyData, simulations: Sequence[EpcSimulation]
+    ) -> Score:
+        cavity = any(
+            part.wall_insulation_type == 2
+            for sim in simulations
+            for part in sim.building_parts.values()
+        )
+        internal = any(
+            part.wall_insulation_type == 3
+            for sim in simulations
+            for part in sim.building_parts.values()
+        )
+        vents = sum(1 for sim in simulations if sim.ventilation is not None)
+        sap = 60.0
+        sap += 5.0 if cavity else 0.0
+        sap += (4.0 if cavity else 0.0) if internal else 0.0
+        sap -= float(vents)
+        return Score(
+            sap_continuous=sap, co2_kg_per_yr=0.0, primary_energy_kwh_per_yr=0.0
+        )
+
+
+def _wall_ventilation_dependency(*, cost: float) -> MeasureDependency:
+    return MeasureDependency(
+        triggers=frozenset(
+            {
+                MeasureType.CAVITY_WALL_INSULATION,
+                MeasureType.INTERNAL_WALL_INSULATION,
+            }
+        ),
+        required=ScoredOption(
+            option=MeasureOption(
+                measure_type=MeasureType.MECHANICAL_VENTILATION,
+                description="mechanical_ventilation",
+                overlay=_VENT_OVERLAY,
+                cost=Cost(total=cost, contingency_rate=0.0),
+            ),
+            sap_gain=0.0,
+        ),
+    )
+
+
+def test_ventilation_dependency_is_injected_once_across_both_phases() -> None:
+    # Arrange — the cavity wall (phase 1) and the internal wall (picked in
+    # phase 2 on its post-cavity worth) both trigger the same forced
+    # ventilation. It must land in the package exactly once — phase 2 sees the
+    # phase-1 dwelling as already ventilated.
+    groups: list[list[ScoredOption]] = [
+        [_scored("cavity_wall_insulation", gain=5.0, cost=1000.0, overlay=_WALL_OVERLAY)],
+        [_scored("internal_wall_insulation", gain=0.0, cost=2000.0, overlay=_IWI_OVERLAY)],
+    ]
+    scorer = _TwoWallScorer()
+
+    # Act — target 68: phase 1 gives 60 + 5 − 1 = 64; the internal wall's
+    # post-fabric +4 closes it, but only if ventilation is not double-counted.
+    package: OptimisedPackage = optimise_package_fabric_first(
+        groups=groups,
+        scorer=scorer,
+        baseline_epc=build_epc(),
+        budget=10000.0,
+        target_sap=68.0,
+        dependencies=[_wall_ventilation_dependency(cost=300.0)],
+    )
+
+    # Assert — one ventilation, and the truthful total counts its penalty once:
+    # 60 + 5 cavity + 4 internal − 1 ventilation = 68.
+    ventilation_count = sum(
+        1
+        for scored in package.selected
+        if scored.option.measure_type == MeasureType.MECHANICAL_VENTILATION
+    )
+    assert ventilation_count == 1
+    assert _selected_types(package) == {
+        "cavity_wall_insulation",
+        "internal_wall_insulation",
+        "mechanical_ventilation",
+    }
+    assert abs(package.score.sap_continuous - 68.0) <= 1e-9
+
+
 class _InteractionScorer:
     """A stub whose boiler gain collapses once the wall is insulated (+10 raw,
     +3 post-fabric) while the heat pump's holds (+8 either way) — so a phase 2