crypto.math module utils: add some tests, fix quick_is_not_prime() for small primes (#733) (#734)

* Fix quick_is_not_prime() for small primes. Add some tests.

* Fix return value of convert_int_to_bytes(0, 0) on Python 2.

* Add some more test cases.

* Simplify the changelog and point out that these errors only happen for cases not happening in regular use.

(cherry picked from commit 0c62837296)

tests/unit/plugins/module_utils/crypto/test_math.py

@@ -0,0 +1,68 @@
+# -*- coding: utf-8 -*-
+
+# Copyright (c) 2024, Felix Fontein <felix@fontein.de>
+# GNU General Public License v3.0+ (see LICENSES/GPL-3.0-or-later.txt or https://www.gnu.org/licenses/gpl-3.0.txt)
+# SPDX-License-Identifier: GPL-3.0-or-later
+
+from __future__ import absolute_import, division, print_function
+__metaclass__ = type
+
+import pytest
+
+from ansible_collections.community.crypto.plugins.module_utils.crypto.math import (
+    binary_exp_mod,
+    simple_gcd,
+    quick_is_not_prime,
+)
+
+
+@pytest.mark.parametrize('f, e, m, result', [
+    (0, 0, 5, 1),
+    (0, 1, 5, 0),
+    (2, 1, 5, 2),
+    (2, 2, 5, 4),
+    (2, 3, 5, 3),
+    (2, 10, 5, 4),
+])
+def test_binary_exp_mod(f, e, m, result):
+    value = binary_exp_mod(f, e, m)
+    print(value)
+    assert value == result
+
+
+@pytest.mark.parametrize('a, b, result', [
+    (0, -123, -123),
+    (0, 123, 123),
+    (-123, 0, -123),
+    (123, 0, 123),
+    (-123, 1, 1),
+    (123, 1, 1),
+    (1, -123, -1),
+    (1, 123, 1),
+    (1024, 10, 2),
+])
+def test_simple_gcd(a, b, result):
+    value = simple_gcd(a, b)
+    print(value)
+    assert value == result
+
+
+@pytest.mark.parametrize('n, result', [
+    (-2, True),
+    (0, True),
+    (1, True),
+    (2, False),
+    (3, False),
+    (4, True),
+    (5, False),
+    (6, True),
+    (7, False),
+    (8, True),
+    (9, True),
+    (10, True),
+    (211, False),  # the smallest prime number >= 200
+])
+def test_quick_is_not_prime(n, result):
+    value = quick_is_not_prime(n)
+    print(value)
+    assert value == result