diff --git a/tests.py b/tests.py
index 3f84b4b..886e1a0 100755
--- a/tests.py
+++ b/tests.py
@@ -17,7 +17,7 @@ from io import BytesIO
 from glob import glob
 from pathlib import Path
 from tempfile import NamedTemporaryFile, TemporaryDirectory
-from typing import cast
+from typing import BinaryIO, cast
 from types import SimpleNamespace
 from unittest.mock import MagicMock, patch
 
@@ -2915,16 +2915,15 @@ class TestMaildirUidHandling(unittest.TestCase):
                 os.makedirs(os.path.join(d, subdir))
 
             original_stat = os.stat
+            call_count = [0]
 
             def stat_that_fails_once(path, *args, **kwargs):
                 """Fail on the first call (UID check), pass through after."""
-                stat_that_fails_once.calls += 1
-                if stat_that_fails_once.calls == 1:
+                call_count[0] += 1
+                if call_count[0] == 1:
                     raise OSError("no stat")
                 return original_stat(path, *args, **kwargs)
 
-            stat_that_fails_once.calls = 0
-
             with patch(
                 "parsedmarc.mail.maildir.os.stat", side_effect=stat_that_fails_once
             ):
@@ -4858,7 +4857,7 @@ class TestExtractReport(unittest.TestCase):
             def close(self):
                 pass
 
-        result = parsedmarc.extract_report(NonSeekable(xml))
+        result = parsedmarc.extract_report(cast(BinaryIO, NonSeekable(xml)))
         self.assertIn("<feedback>", result)
 
     def testExtractReportInvalidContent(self):
@@ -4883,7 +4882,7 @@ class TestExtractReport(unittest.TestCase):
                 pass
 
         with self.assertRaises(parsedmarc.ParserError):
-            parsedmarc.extract_report(TextStream())
+            parsedmarc.extract_report(cast(BinaryIO, TextStream()))
 
 
 class TestMalformedXmlRecovery(unittest.TestCase):
@@ -4941,7 +4940,7 @@ class TestMalformedXmlRecovery(unittest.TestCase):
     <auth_results><spf><domain>example.com</domain><result>pass</result></spf></auth_results>
   </record>
 </feedback>"""
-        report = parsedmarc.parse_aggregate_report_xml(xml, offline=True)
+        report = parsedmarc.parse_aggregate_report_xml(xml.decode(), offline=True)
         self.assertEqual(report["report_metadata"]["report_id"], "test-bytes-input")
 
     def testExpatErrorRaises(self):
@@ -5195,7 +5194,7 @@ Test body"""
     def testMissingVersion(self):
         """Missing version defaults to None"""
         report_str = self._make_feedback_report()
-        lines = [l for l in report_str.split("\n") if not l.startswith("Version:")]
+        lines = [ln for ln in report_str.split("\n") if not ln.startswith("Version:")]
         report_str = "\n".join(lines)
         report = parsedmarc.parse_failure_report(
             report_str, self._make_sample(), self._default_msg_date(), offline=True
@@ -5205,7 +5204,7 @@ Test body"""
     def testMissingUserAgent(self):
         """Missing user_agent defaults to None"""
         report_str = self._make_feedback_report()
-        lines = [l for l in report_str.split("\n") if not l.startswith("User-Agent:")]
+        lines = [ln for ln in report_str.split("\n") if not ln.startswith("User-Agent:")]
         report_str = "\n".join(lines)
         report = parsedmarc.parse_failure_report(
             report_str, self._make_sample(), self._default_msg_date(), offline=True
@@ -5259,7 +5258,7 @@ Test body"""
         """Missing reported_domain falls back to sample from domain"""
         report_str = self._make_feedback_report()
         lines = [
-            l for l in report_str.split("\n") if not l.startswith("Reported-Domain:")
+            ln for ln in report_str.split("\n") if not ln.startswith("Reported-Domain:")
         ]
         report_str = "\n".join(lines)
         report = parsedmarc.parse_failure_report(
@@ -5270,7 +5269,7 @@ Test body"""
     def testMissingArrivalDateWithMsgDate(self):
         """Missing arrival_date uses msg_date fallback"""
         report_str = self._make_feedback_report()
-        lines = [l for l in report_str.split("\n") if not l.startswith("Arrival-Date:")]
+        lines = [ln for ln in report_str.split("\n") if not ln.startswith("Arrival-Date:")]
         report_str = "\n".join(lines)
         msg_date = datetime(2024, 6, 15, 12, 0, 0, tzinfo=timezone.utc)
         report = parsedmarc.parse_failure_report(
@@ -5281,11 +5280,14 @@ Test body"""
     def testMissingArrivalDateNoMsgDateRaises(self):
         """Missing arrival_date with no msg_date raises"""
         report_str = self._make_feedback_report()
-        lines = [l for l in report_str.split("\n") if not l.startswith("Arrival-Date:")]
+        lines = [ln for ln in report_str.split("\n") if not ln.startswith("Arrival-Date:")]
         report_str = "\n".join(lines)
         with self.assertRaises(parsedmarc.InvalidFailureReport):
             parsedmarc.parse_failure_report(
-                report_str, self._make_sample(), None, offline=True
+                report_str,
+                self._make_sample(),
+                cast(datetime, None),  # intentionally None to test error path
+                offline=True,
             )
 
 
@@ -5422,7 +5424,6 @@ Body"""
 
     def testEmailWithAttachments(self):
         """parse_email with strip_attachment_payloads removes payloads"""
-        import email as email_mod
         from email.mime.multipart import MIMEMultipart
         from email.mime.text import MIMEText
         from email.mime.base import MIMEBase
@@ -5551,7 +5552,6 @@ class TestGetDmarcReportsFromMbox(unittest.TestCase):
 
     def testMboxWithAggregateReport(self):
         """Mbox with aggregate report email is parsed"""
-        import email as email_mod
         from email.mime.multipart import MIMEMultipart
         from email.mime.application import MIMEApplication
         import gzip