diff --git a/pyas2lib/utils.py b/pyas2lib/utils.py
index 40e985e..d289795 100644
--- a/pyas2lib/utils.py
+++ b/pyas2lib/utils.py
@@ -191,7 +191,9 @@ def verify_certificate_chain(cert_str, trusted_certs, ignore_self_signed=True):
 def extract_certificate_info(cert):
     """
     Extract validity information from the certificate and return a dictionary.
-    Provide either key with certificate (private) or public certificate
+
+    Provide either key with certificate (private) or public certificate.
+
     :param cert: the certificate as byte string in PEM or DER format
     :return: a dictionary holding certificate information:
                 valid_from (datetime)
@@ -216,16 +218,21 @@ def extract_certificate_info(cert):
     # iterate through the list to find the certificate
     for _item in der:
         try:
-            # load the certificate. if element is key, exception is triggered and next element is tried
+            # load the certificate. if element is key, exception is triggered
+            # and next element is tried
             certificate = crypto.load_certificate(crypto.FILETYPE_ASN1, _item)
 
             # on successful load, extract the various fields into the dictionary
-            cert_info['valid_from'] = datetime.strptime(certificate.get_notBefore().decode('utf8'), "%Y%m%d%H%M%SZ")
-            cert_info['valid_to'] = datetime.strptime(certificate.get_notAfter().decode('utf8'), "%Y%m%d%H%M%SZ")
-            cert_info['subject'] = [tuple(item.decode('utf8') for item in sets)
-                                    for sets in certificate.get_subject().get_components()]
-            cert_info['issuer'] = [tuple(item.decode('utf8') for item in sets)
-                                   for sets in certificate.get_issuer().get_components()]
+            cert_info['valid_from'] = datetime.strptime(
+                certificate.get_notBefore().decode('utf8'), "%Y%m%d%H%M%SZ")
+            cert_info['valid_to'] = datetime.strptime(
+                certificate.get_notAfter().decode('utf8'), "%Y%m%d%H%M%SZ")
+            cert_info['subject'] = [
+                tuple(item.decode('utf8') for item in sets)
+                for sets in certificate.get_subject().get_components()]
+            cert_info['issuer'] = [
+                tuple(item.decode('utf8') for item in sets)
+                for sets in certificate.get_issuer().get_components()]
             cert_info['serial'] = certificate.get_serial_number()
             break
         except crypto.Error:
diff --git a/tests/test_advanced.py b/tests/test_advanced.py
index ce39ce3..06fd12f 100644
--- a/tests/test_advanced.py
+++ b/tests/test_advanced.py
@@ -4,6 +4,7 @@
 import base64
 import datetime
 
+
 class TestAdvanced(Pyas2TestCase):
 
     def setUp(self):
@@ -72,7 +73,7 @@ def test_partner_not_found(self):
         _, _, mdn = in_message.parse(
             raw_out_message,
             find_org_cb=self.find_org,
-            find_partner_cb=self.find_none,
+            find_partner_cb=lambda x: None,
             find_message_cb=lambda x, y: False
         )
 
@@ -88,7 +89,7 @@ def test_partner_not_found(self):
         in_message = as2.Message()
         _, _, mdn = in_message.parse(
             raw_out_message,
-            find_org_cb=self.find_none,
+            find_org_cb=lambda x: None,
             find_partner_cb=self.find_partner,
             find_message_cb=lambda x, y: False
         )
@@ -326,36 +327,43 @@ def test_load_private_key(self):
                 self.fail('Failed to load pem private key: %s' % e)
 
     def test_extract_certificate_info(self):
-        """ Test case that extracts data from private and public certificates in PEM or DER format"""
-
-        cert_info = {'valid_from': datetime.datetime(2019, 6, 3, 11, 32, 57),
-                     'valid_to': datetime.datetime(2029, 5, 31, 11, 32, 57),
-                     'subject': [('C', 'AU'), ('ST', 'Some-State'), ('O', 'pyas2lib'), ('CN', 'test')],
-                     'issuer': [('C', 'AU'), ('ST', 'Some-State'), ('O', 'pyas2lib'), ('CN', 'test')],
-                     'serial': 13747137503594840569}
-        cert_empty = {'valid_from': None,
-                     'valid_to': None,
-                     'subject': None,
-                     'issuer': None,
-                     'serial': None}
+        """ Test case that extracts data from private and public certificates
+         in PEM or DER format"""
+
+        cert_info = {
+            'valid_from': datetime.datetime(2019, 6, 3, 11, 32, 57),
+            'valid_to': datetime.datetime(2029, 5, 31, 11, 32, 57),
+            'subject': [('C', 'AU'), ('ST', 'Some-State'),
+                        ('O', 'pyas2lib'), ('CN', 'test')],
+            'issuer': [('C', 'AU'), ('ST', 'Some-State'),
+                       ('O', 'pyas2lib'), ('CN', 'test')],
+            'serial': 13747137503594840569
+        }
+        cert_empty = {
+            'valid_from': None,
+            'valid_to': None,
+            'subject': None,
+            'issuer': None,
+            'serial': None
+        }
 
         # compare result of function with cert_info dict.
-        self.assertEqual(utils.extract_certificate_info(self.private_pem), cert_info)
-        self.assertEqual(utils.extract_certificate_info(self.private_cer), cert_info)
-        self.assertEqual(utils.extract_certificate_info(self.public_pem), cert_info)
-        self.assertEqual(utils.extract_certificate_info(self.public_cer), cert_info)
+        self.assertEqual(
+            utils.extract_certificate_info(self.private_pem), cert_info)
+        self.assertEqual(
+            utils.extract_certificate_info(self.private_cer), cert_info)
+        self.assertEqual(
+            utils.extract_certificate_info(self.public_pem), cert_info)
+        self.assertEqual(
+            utils.extract_certificate_info(self.public_cer), cert_info)
         self.assertEqual(utils.extract_certificate_info(b''), cert_empty)
 
-
     def find_org(self, headers):
         return self.org
 
     def find_partner(self, headers):
         return self.partner
 
-    def find_none(self, as2_id):
-        return None
-
     def find_message(self, message_id, message_recipient):
         return self.out_message