test(fixtures): build_epc() deep-copies its windows so callers can't leak state

The worksheet build_epc() fixtures wrapped a module-level SECTION_6_VERTICAL_
WINDOWS tuple in list(), so every call returned the SAME SapWindow objects. A
test that mutated a returned window (the glazing slices flip glazing_type to
single) leaked that change into every later build_epc() -- which surfaced as
double_glazing-product failures in the first-run integration tests only when
test_console ran first in the same process.

Deep-copy the windows per call in all six fixtures (000474/477/480/487/490/516)
so each EpcPropertyData owns an independent window graph, and drop the
now-redundant defensive copy at the glazing test's call site.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

tests/domain/sap10_calculator/worksheet/_elmhurst_worksheet_000474.py

@@ -19,6 +19,7 @@ Distinct features vs prior fixtures:
   first 5.27) — the upper storey is smaller than the ground
 """
 
+import copy
 from typing import Optional
 
 from datatypes.epc.domain.epc_property_data import (
@@ -164,7 +165,10 @@ def build_epc() -> EpcPropertyData:
         heated_rooms_count=3,
         door_count=2,
         low_energy_fixed_lighting_bulbs_count=8,
-        sap_windows=list(SECTION_6_VERTICAL_WINDOWS),
+        # Deep-copy so each build_epc() owns its windows (the module-level
+        # SECTION_6_VERTICAL_WINDOWS tuple holds shared SapWindow objects; a
+        # caller mutating a returned window would otherwise leak across calls).
+        sap_windows=[copy.deepcopy(window) for window in SECTION_6_VERTICAL_WINDOWS],
         percent_draughtproofed=78,
         extensions_count=2,
         blocked_chimneys_count=0,

tests/domain/sap10_calculator/worksheet/_elmhurst_worksheet_000477.py

@@ -15,6 +15,7 @@ Distinct features vs prior fixtures:
   flat ceiling — just stud walls (1.5/1.3 height) + slopes
 """
 
+import copy
 from typing import Optional
 
 from datatypes.epc.domain.epc_property_data import (
@@ -137,7 +138,10 @@ def build_epc() -> EpcPropertyData:
         door_count=2,
         percent_draughtproofed=100,
         low_energy_fixed_lighting_bulbs_count=SECTION_5_BULB_COUNT_LEL,
-        sap_windows=list(SECTION_6_VERTICAL_WINDOWS),
+        # Deep-copy so each build_epc() owns its windows (the module-level
+        # SECTION_6_VERTICAL_WINDOWS tuple holds shared SapWindow objects; a
+        # caller mutating a returned window would otherwise leak across calls).
+        sap_windows=[copy.deepcopy(window) for window in SECTION_6_VERTICAL_WINDOWS],
         blocked_chimneys_count=0,
         dwelling_type="Mid-Terrace house",
         built_form="Mid-Terrace",

tests/domain/sap10_calculator/worksheet/_elmhurst_worksheet_000480.py

@@ -16,6 +16,7 @@ Differs from 000487 along several useful axes:
 - No alternative wall (vs 1 timber-frame alt wall on the extension)
 """
 
+import copy
 from typing import Optional
 
 from datatypes.epc.domain.epc_property_data import (
@@ -180,7 +181,10 @@ def build_epc() -> EpcPropertyData:
         door_count=2,  # cert lodges 2 doors total
         percent_draughtproofed=100,
         low_energy_fixed_lighting_bulbs_count=SECTION_5_BULB_COUNT_LEL,
-        sap_windows=list(SECTION_6_VERTICAL_WINDOWS),
+        # Deep-copy so each build_epc() owns its windows (the module-level
+        # SECTION_6_VERTICAL_WINDOWS tuple holds shared SapWindow objects; a
+        # caller mutating a returned window would otherwise leak across calls).
+        sap_windows=[copy.deepcopy(window) for window in SECTION_6_VERTICAL_WINDOWS],
         extensions_count=1,
         blocked_chimneys_count=0,
         dwelling_type="Mid-Terrace house",

tests/domain/sap10_calculator/worksheet/_elmhurst_worksheet_000487.py

@@ -13,6 +13,7 @@ values captured below. Treat the LINE_X constants as authoritative; if
 they diverge from our code, the bug is on our side.
 """
 
+import copy
 from typing import Optional
 
 from datatypes.epc.domain.epc_property_data import (
@@ -190,7 +191,10 @@ def build_epc() -> EpcPropertyData:
         door_count=1,
         percent_draughtproofed=100,
         low_energy_fixed_lighting_bulbs_count=SECTION_5_BULB_COUNT_LEL,
-        sap_windows=list(SECTION_6_VERTICAL_WINDOWS),
+        # Deep-copy so each build_epc() owns its windows (the module-level
+        # SECTION_6_VERTICAL_WINDOWS tuple holds shared SapWindow objects; a
+        # caller mutating a returned window would otherwise leak across calls).
+        sap_windows=[copy.deepcopy(window) for window in SECTION_6_VERTICAL_WINDOWS],
         extensions_count=1,
         blocked_chimneys_count=0,
         dwelling_type="Enclosed Mid-Terrace house",

tests/domain/sap10_calculator/worksheet/_elmhurst_worksheet_000490.py

@@ -21,6 +21,7 @@ Distinct features vs prior fixtures:
 - DP = 100%, so (15) = 0.05 (lowest window-infiltration component)
 """
 
+import copy
 from typing import Optional
 
 from datatypes.epc.domain.epc_property_data import (
@@ -146,7 +147,11 @@ def build_epc() -> EpcPropertyData:
         heated_rooms_count=4,
         door_count=2,
         low_energy_fixed_lighting_bulbs_count=8,
-        sap_windows=list(SECTION_6_VERTICAL_WINDOWS),
+        # Deep-copy so each build_epc() owns its windows: SECTION_6_VERTICAL_
+        # WINDOWS is a module-level tuple of shared SapWindow objects, and a
+        # caller that mutates a returned window (e.g. flipping glazing_type to
+        # test a glazing measure) would otherwise leak into every later call.
+        sap_windows=[copy.deepcopy(window) for window in SECTION_6_VERTICAL_WINDOWS],
         percent_draughtproofed=100,
         extensions_count=1,
         blocked_chimneys_count=0,

tests/domain/sap10_calculator/worksheet/_elmhurst_worksheet_000516.py

@@ -21,6 +21,7 @@ Distinct features vs prior fixtures:
   as 000480 but on a single-part dwelling
 """
 
+import copy
 from typing import Optional
 
 from datatypes.epc.domain.epc_property_data import (
@@ -175,7 +176,10 @@ def build_epc() -> EpcPropertyData:
         ],
         percent_draughtproofed=75,
         low_energy_fixed_lighting_bulbs_count=SECTION_5_BULB_COUNT_LEL,
-        sap_windows=list(SECTION_6_VERTICAL_WINDOWS),
+        # Deep-copy so each build_epc() owns its windows (the module-level
+        # SECTION_6_VERTICAL_WINDOWS tuple holds shared SapWindow objects; a
+        # caller mutating a returned window would otherwise leak across calls).
+        sap_windows=[copy.deepcopy(window) for window in SECTION_6_VERTICAL_WINDOWS],
         blocked_chimneys_count=0,
         dwelling_type="Mid-Terrace house",
         built_form="Mid-Terrace",

tests/harness/test_console.py

@@ -2,7 +2,6 @@
 
 from __future__ import annotations
 
-import copy
 import dataclasses
 
 import pytest
@@ -117,11 +116,8 @@ def test_run_modelling_listed_building_yields_no_wall_insulation() -> None:
 
 def _single_glazed_epc() -> EpcPropertyData:
     """The cavity/floor dwelling with all windows single-glazed — the glazing
-    generator's trigger, sized so the upgrade reaches the optimised package.
-
-    `build_epc()` shares its window objects across calls, so deep-copy before
-    mutating to avoid leaking single-glazing into other tests' baselines."""
-    epc: EpcPropertyData = copy.deepcopy(_build_uninsulated_cavity_and_floor_epc())
+    generator's trigger, sized so the upgrade reaches the optimised package."""
+    epc: EpcPropertyData = _build_uninsulated_cavity_and_floor_epc()
     for window in epc.sap_windows:
         window.glazing_type = 1  # SAP10.2 Table U2 code 1 = single.
     return epc