diff --git a/src/icalendar/cal.py b/src/icalendar/cal.py
index bae86bd8..ebd60efc 100644
--- a/src/icalendar/cal.py
+++ b/src/icalendar/cal.py
@@ -491,6 +491,7 @@ def from_ical(cls, st, multiple=False):
                 'Found no components where exactly one is required', st))
         return comps[0]
 
+    @staticmethod
     def _format_error(error_description, bad_input, elipsis='[...]'):
         # there's three character more in the error, ie. ' ' x2 and a ':'
         max_error_length = 100 - 3
diff --git a/src/icalendar/parser_tools.py b/src/icalendar/parser_tools.py
index 28b22fc5..cb99f427 100644
--- a/src/icalendar/parser_tools.py
+++ b/src/icalendar/parser_tools.py
@@ -1,4 +1,4 @@
-from typing import Any, Union
+from typing import List, Union
 
 SEQUENCE_TYPES = (list, tuple)
 DEFAULT_ENCODING = 'utf-8'
@@ -35,7 +35,9 @@ def to_unicode(value: ICAL_TYPE, encoding='utf-8-sig') -> str:
     return value
 
 
-def data_encode(data: Union[ICAL_TYPE, dict, list], encoding=DEFAULT_ENCODING) -> bytes:
+def data_encode(
+        data: Union[ICAL_TYPE, dict, list], encoding=DEFAULT_ENCODING
+) -> Union[bytes, List[bytes], dict]:
     """Encode all datastructures to the given encoding.
     Currently unicode strings, dicts and lists are supported.
     """
diff --git a/src/icalendar/tests/fuzzed/__init__.py b/src/icalendar/tests/fuzzed/__init__.py
index 17048e6d..2b7e1e4c 100644
--- a/src/icalendar/tests/fuzzed/__init__.py
+++ b/src/icalendar/tests/fuzzed/__init__.py
@@ -19,7 +19,7 @@ def fuzz_calendar_v1(
         cal = [cal]
     for c in cal:
         if should_walk:
-            for event in cal.walk("VEVENT"):
+            for event in c.walk("VEVENT"):
                 event.to_ical()
         else:
-            cal.to_ical()
+            c.to_ical()
diff --git a/src/icalendar/tests/prop/test_windows_to_olson_mapping.py b/src/icalendar/tests/prop/test_windows_to_olson_mapping.py
index 2202c589..489d0d23 100644
--- a/src/icalendar/tests/prop/test_windows_to_olson_mapping.py
+++ b/src/icalendar/tests/prop/test_windows_to_olson_mapping.py
@@ -12,7 +12,7 @@ def test_windows_timezone(tzp):
     """Test that the timezone is mapped correctly to olson."""
     dt = vDatetime.from_ical("20170507T181920", "Eastern Standard Time")
     expected = tzp.localize(datetime(2017, 5, 7, 18, 19, 20), "America/New_York")
-    assert dt.tzinfo == dt.tzinfo
+    assert dt.tzinfo == expected.tzinfo
     assert dt == expected
 
 
diff --git a/src/icalendar/tests/test_issue_722_generate_vtimezone.py b/src/icalendar/tests/test_issue_722_generate_vtimezone.py
index 31e7f27f..173a0295 100644
--- a/src/icalendar/tests/test_issue_722_generate_vtimezone.py
+++ b/src/icalendar/tests/test_issue_722_generate_vtimezone.py
@@ -56,7 +56,7 @@ def test_conversion_converges(tzp, tzid):
     tzinfo2 = generated1.to_tz()
     generated2 = Timezone.from_tzinfo(tzinfo2, "test-generated")
     tzinfo3 = generated2.to_tz()
-    generated3 = Timezone.from_tzinfo(tzinfo2, "test-generated")
+    generated3 = Timezone.from_tzinfo(tzinfo3, "test-generated")
     # pprint(generated1.get_transitions())
     # pprint(generated2.get_transitions())
     assert_components_equal(generated1, generated2)
diff --git a/src/icalendar/timezone/equivalent_timezone_ids.py b/src/icalendar/timezone/equivalent_timezone_ids.py
index 63da737e..affdb2ec 100644
--- a/src/icalendar/timezone/equivalent_timezone_ids.py
+++ b/src/icalendar/timezone/equivalent_timezone_ids.py
@@ -20,7 +20,7 @@
 from pathlib import Path
 from pprint import pprint
 from time import time
-from typing import Callable, NamedTuple, Optional
+from typing import Callable, NamedTuple, Optional, Any, Tuple, List
 
 from zoneinfo import ZoneInfo, available_timezones
 
@@ -30,7 +30,7 @@
 def check(dt, tz:tzinfo):
     return (dt, tz.utcoffset(dt))
 
-def checks(tz:tzinfo) -> tuple:
+def checks(tz:tzinfo) -> List[Tuple[Any, Optional[timedelta]]]:
     result = []
     for dt in DTS:
         try: