feat(fusion_accounting_reports): currency conversion service

Pure-Python helper for FX conversion at report end-date. Handles direct
rates, inverse rates, and fallback to most-recent-rate-on-or-before.
fetch_rates() pulls from res.currency.rate using the same
1/rate inversion convention Odoo uses internally.

Made-with: Cursor

fusion_accounting_reports/tests/__init__.py

@@ -1 +1,2 @@
 from . import test_services_unit
+from . import test_currency_conversion

fusion_accounting_reports/tests/test_currency_conversion.py

@@ -0,0 +1,53 @@
+"""Unit tests for currency_conversion service."""
+
+from datetime import date
+
+from odoo.tests.common import TransactionCase, tagged
+from odoo.addons.fusion_accounting_reports.services.currency_conversion import (
+    convert_amount, fetch_rates,
+)
+
+
+@tagged('post_install', '-at_install')
+class TestCurrencyConversion(TransactionCase):
+
+    def test_same_currency_returns_unchanged(self):
+        result = convert_amount(100, source_currency='USD',
+                                target_currency='USD',
+                                rate_date=date(2026, 4, 19), rates={})
+        self.assertEqual(result, 100)
+
+    def test_direct_rate(self):
+        rates = {('USD', 'CAD', date(2026, 4, 19)): 1.35}
+        result = convert_amount(100, source_currency='USD',
+                                target_currency='CAD',
+                                rate_date=date(2026, 4, 19), rates=rates)
+        self.assertEqual(result, 135)
+
+    def test_inverse_rate(self):
+        rates = {('CAD', 'USD', date(2026, 4, 19)): 0.74}
+        result = convert_amount(100, source_currency='USD',
+                                target_currency='CAD',
+                                rate_date=date(2026, 4, 19), rates=rates)
+        self.assertAlmostEqual(result, 100 / 0.74, places=2)
+
+    def test_falls_back_to_most_recent_rate(self):
+        rates = {
+            ('USD', 'CAD', date(2026, 1, 1)): 1.30,
+            ('USD', 'CAD', date(2026, 3, 1)): 1.32,
+        }
+        result = convert_amount(100, source_currency='USD',
+                                target_currency='CAD',
+                                rate_date=date(2026, 4, 19), rates=rates)
+        self.assertEqual(result, 132)
+
+    def test_raises_when_no_rate(self):
+        with self.assertRaises(ValueError):
+            convert_amount(100, source_currency='EUR',
+                           target_currency='CAD',
+                           rate_date=date(2026, 4, 19), rates={})
+
+    def test_fetch_rates_from_env(self):
+        cad = self.env.ref('base.CAD')
+        rates = fetch_rates(self.env, target_currency_id=cad.id, as_of=date(2026, 4, 19))
+        self.assertIsInstance(rates, dict)