From a6533fea7a64f9676dfc3dab8816be43f28bbbd9 Mon Sep 17 00:00:00 2001
From: Yuki Morikawa <193417531+Doyoubelieveinfate@users.noreply.github.com>
Date: Tue, 20 Oct 2026 22:59:28 +0900
Subject: [PATCH] Require both check digits for individual INNs

---
 src/validators/i18n/ru.py |  8 +-------
 tests/i18n/test_ru.py     | 19 +++++++++++++++++++
 2 files changed, 20 insertions(+), 7 deletions(-)

diff --git a/src/validators/i18n/ru.py b/src/validators/i18n/ru.py
index 0df5fce0..2b6da7f2 100644
--- a/src/validators/i18n/ru.py
+++ b/src/validators/i18n/ru.py
@@ -50,13 +50,7 @@ def ru_inn(value: str):
             control_number1 = sum([d * w for d, w in zip(digits, weight_coefs1)]) % 11
             weight_coefs2 = [3, 7, 2, 4, 10, 3, 5, 9, 4, 6, 8, 0]
             control_number2 = sum([d * w for d, w in zip(digits, weight_coefs2)]) % 11
-            return (
-                (control_number1 % 10) == digits[-2]
-                if control_number1 > 9
-                else control_number1 == digits[-2] and (control_number2 % 10) == digits[-1]
-                if control_number2 > 9
-                else control_number2 == digits[-1]
-            )
+            return (control_number1 % 10) == digits[-2] and (control_number2 % 10) == digits[-1]
         else:
             return False
     except ValueError:
diff --git a/tests/i18n/test_ru.py b/tests/i18n/test_ru.py
index 1f111087..5c7017e4 100644
--- a/tests/i18n/test_ru.py
+++ b/tests/i18n/test_ru.py
@@ -46,3 +46,22 @@ def test_returns_true_on_valid_ru_inn(value: str):
 def test_returns_false_on_valid_ru_inn(value: str):
     """Test returns true on valid russian individual tax number."""
     assert isinstance(ru_inn(value), ValidationError)
+
+
+@pytest.mark.parametrize(
+    "value",
+    [
+        "500100732266",  # First check digit is wrong; the second matches.
+        "100000001103",  # First remainder is 10; the second check digit is wrong.
+        "100000000781",  # Second remainder is 10; its check digit must be zero.
+    ],
+)
+def test_individual_inn_requires_both_check_digits(value: str):
+    """Reject an individual INN when either check digit is wrong."""
+    assert isinstance(ru_inn(value), ValidationError)
+
+
+@pytest.mark.parametrize("value", ["500100732259", "100000001102", "100000000780"])
+def test_individual_inn_check_digit_remainders(value: str):
+    """Accept both ordinary remainders and remainder 10 mapped to zero."""
+    assert ru_inn(value) is True