Be resilient against the situation when no erorr happened.

Fixes #258.

2 files changed, 29 insertions, 0 deletions

diff --git a/tests/alltests.py b/tests/alltests.py
index a0e7739..141cd88 100644
--- a/tests/alltests.py
+++ b/tests/alltests.py
@@ -32,6 +32,7 @@ def suite():
         'tests.test_dh',
         'tests.test_dsa',
         'tests.test_engine',
+        'tests.test_err',
         'tests.test_evp',
         'tests.test_obj',
         'tests.test_rand',
diff --git a/tests/test_err.py b/tests/test_err.py
new file mode 100644
index 0000000..05fe425
--- /dev/null
+++ b/tests/test_err.py
@@ -0,0 +1,28 @@
+#!/usr/bin/env python
+# -*- coding: utf-8 -*-
+"""Unit tests for M2Crypto.Err.
+
+Copyright (C) 2019 Matěj Cepl
+Released under the terms of MIT/X11 License,
+see the file LICENCE for more.
+"""
+from M2Crypto import Err
+from tests import unittest
+
+
+class ErrTestCase(unittest.TestCase):
+
+    def test_no_error(self):
+        # Protection against gl#m2crypto/m2crypto#258
+        self.assertEqual(Err.get_error_reason(0), '')
+
+
+
+def suite():
+    suite = unittest.TestSuite()
+    suite.addTest(unittest.makeSuite(ErrTestCase))
+    return suite
+
+
+if __name__ == '__main__':
+    unittest.TextTestRunner().run(suite())