From 1e70b8d5c06db8e596da9d4b7a0e046fb75f8b84 Mon Sep 17 00:00:00 2001
From: gsinghpal <gur_preet.singh@outlook.com>
Date: Sun, 19 Apr 2026 17:22:55 -0400
Subject: [PATCH] test(fusion_accounting_assets): Hypothesis property-based
 depreciation invariants

Made-with: Cursor
---
 fusion_accounting_assets/tests/__init__.py    |   1 +
 .../tests/test_engine_property.py             | 101 ++++++++++++++++++
 2 files changed, 102 insertions(+)
 create mode 100644 fusion_accounting_assets/tests/test_engine_property.py

diff --git a/fusion_accounting_assets/tests/__init__.py b/fusion_accounting_assets/tests/__init__.py
index 9a0e65ee..2acadf6e 100644
--- a/fusion_accounting_assets/tests/__init__.py
+++ b/fusion_accounting_assets/tests/__init__.py
@@ -15,3 +15,4 @@ from . import test_assets_controller
 from . import test_assets_adapter
 from . import test_asset_tools
 from . import test_assets_cron
+from . import test_engine_property
diff --git a/fusion_accounting_assets/tests/test_engine_property.py b/fusion_accounting_assets/tests/test_engine_property.py
new file mode 100644
index 00000000..e211b4a1
--- /dev/null
+++ b/fusion_accounting_assets/tests/test_engine_property.py
@@ -0,0 +1,101 @@
+"""Property-based invariant tests for the asset engine.
+
+Hypothesis generates random inputs; we assert mathematical invariants
+that must hold regardless of input."""
+
+from hypothesis import given, settings, strategies as st, HealthCheck
+from odoo.tests.common import TransactionCase
+from odoo.tests import tagged
+
+from odoo.addons.fusion_accounting_assets.services.depreciation_methods import (
+    straight_line, declining_balance, units_of_production,
+)
+
+
+@tagged('post_install', '-at_install', 'property_based')
+class TestDepreciationInvariants(TransactionCase):
+
+    @given(
+        cost=st.floats(min_value=100.0, max_value=1000000.0,
+                       allow_nan=False, allow_infinity=False),
+        salvage_pct=st.floats(min_value=0.0, max_value=0.5,
+                              allow_nan=False, allow_infinity=False),
+        n_periods=st.integers(min_value=1, max_value=40),
+    )
+    @settings(max_examples=80, deadline=2000,
+              suppress_health_check=[HealthCheck.function_scoped_fixture])
+    def test_straight_line_total_equals_cost_minus_salvage(self, cost, salvage_pct, n_periods):
+        cost = round(cost, 2)
+        salvage = round(cost * salvage_pct, 2)
+        steps = straight_line(cost=cost, salvage_value=salvage, n_periods=n_periods)
+        total = sum(s.period_amount for s in steps)
+        # Within 1c rounding tolerance
+        self.assertAlmostEqual(
+            total, cost - salvage, places=1,
+            msg=f"cost={cost}, salvage={salvage}, n={n_periods}, total={total:.2f}",
+        )
+
+    @given(
+        cost=st.floats(min_value=100.0, max_value=1000000.0,
+                       allow_nan=False, allow_infinity=False),
+        salvage_pct=st.floats(min_value=0.0, max_value=0.5,
+                              allow_nan=False, allow_infinity=False),
+        n_periods=st.integers(min_value=1, max_value=20),
+    )
+    @settings(max_examples=50, deadline=2000,
+              suppress_health_check=[HealthCheck.function_scoped_fixture])
+    def test_straight_line_book_value_decreasing(self, cost, salvage_pct, n_periods):
+        cost = round(cost, 2)
+        salvage = round(cost * salvage_pct, 2)
+        steps = straight_line(cost=cost, salvage_value=salvage, n_periods=n_periods)
+        for i in range(1, len(steps)):
+            self.assertLessEqual(
+                steps[i].book_value_at_end,
+                steps[i - 1].book_value_at_end + 0.01,
+            )
+
+    @given(
+        cost=st.floats(min_value=1000.0, max_value=100000.0,
+                       allow_nan=False, allow_infinity=False),
+        salvage_pct=st.floats(min_value=0.0, max_value=0.3,
+                              allow_nan=False, allow_infinity=False),
+        n_periods=st.integers(min_value=2, max_value=20),
+        rate=st.floats(min_value=0.05, max_value=0.5,
+                       allow_nan=False, allow_infinity=False),
+    )
+    @settings(max_examples=50, deadline=3000,
+              suppress_health_check=[HealthCheck.function_scoped_fixture])
+    def test_declining_balance_never_below_salvage(self, cost, salvage_pct, n_periods, rate):
+        cost = round(cost, 2)
+        salvage = round(cost * salvage_pct, 2)
+        steps = declining_balance(
+            cost=cost, salvage_value=salvage,
+            n_periods=n_periods, rate=rate,
+        )
+        for s in steps:
+            self.assertGreaterEqual(
+                s.book_value_at_end, salvage - 0.01,
+                msg=f"cost={cost}, salvage={salvage}, rate={rate}, step={s}",
+            )
+
+    @given(
+        cost=st.floats(min_value=1000.0, max_value=100000.0,
+                       allow_nan=False, allow_infinity=False),
+        total_units=st.floats(min_value=100.0, max_value=10000.0,
+                              allow_nan=False, allow_infinity=False),
+        n_periods=st.integers(min_value=1, max_value=10),
+    )
+    @settings(max_examples=30, deadline=2000,
+              suppress_health_check=[HealthCheck.function_scoped_fixture])
+    def test_units_of_production_total_at_full_use_equals_depreciable(self, cost, total_units, n_periods):
+        cost = round(cost, 2)
+        salvage = 0.0
+        # Distribute total_units evenly across periods
+        per_period = total_units / n_periods
+        steps = units_of_production(
+            cost=cost, salvage_value=salvage,
+            total_units_expected=total_units,
+            units_per_period=[per_period] * n_periods,
+        )
+        total = sum(s.period_amount for s in steps)
+        self.assertAlmostEqual(total, cost - salvage, places=1)