diff --git a/asserts/__init__.py b/asserts/__init__.py
index 1c65ecf..410e8dc 100644
--- a/asserts/__init__.py
+++ b/asserts/__init__.py
@@ -20,12 +20,14 @@
 
 """
 
+from __future__ import annotations
+
 import re
 import sys
 from datetime import datetime, timedelta
 from json import loads as json_loads
-from typing import Set
-from warnings import catch_warnings
+from typing import Any, Callable, Set
+from warnings import WarningMessage, catch_warnings
 
 
 def fail(msg=None):
@@ -864,7 +866,7 @@ def assert_datetime_about_now_utc(actual, msg_fmt="{msg}"):
         fail(msg_fmt.format(msg=msg, actual=actual, now=now))
 
 
-class AssertRaisesContext(object):
+class AssertRaisesContext:
     """A context manager to test for exceptions with certain properties.
 
     When the context is left and no exception has been raised, an
@@ -906,7 +908,7 @@ def __init__(self, exception, msg_fmt="{msg}"):
         self._exc_type = exception
         self._exc_val = None
         self._exception_name = getattr(exception, "__name__", str(exception))
-        self._tests = []
+        self._tests: list[Callable[[Any], object]] = []
 
     def __enter__(self):
         return self
@@ -929,7 +931,7 @@ def format_message(self, default_msg):
             exc_name=self._exception_name,
         )
 
-    def add_test(self, cb):
+    def add_test(self, cb: Callable[[Any], object]) -> None:
         """Add a test callback.
 
         This callback is called after determining that the right exception
@@ -1188,9 +1190,11 @@ class AssertWarnsContext(object):
     def __init__(self, warning_class, msg_fmt="{msg}"):
         self._warning_class = warning_class
         self._msg_fmt = msg_fmt
-        self._warning_context = None
+        self._warning_context: catch_warnings[list[WarningMessage]] | None = (
+            None
+        )
         self._warnings = []
-        self._tests = []
+        self._tests: list[Callable[[Warning], bool]] = []
 
     def __enter__(self):
         self._warning_context = catch_warnings(record=True)
@@ -1198,6 +1202,7 @@ def __enter__(self):
         return self
 
     def __exit__(self, exc_type, exc_val, exc_tb):
+        assert self._warning_context is not None
         self._warning_context.__exit__(exc_type, exc_val, exc_tb)
         if not any(self._is_expected_warning(w) for w in self._warnings):
             fail(self.format_message())
@@ -1210,12 +1215,12 @@ def format_message(self):
             exc_name=self._warning_class.__name__,
         )
 
-    def _is_expected_warning(self, warning):
+    def _is_expected_warning(self, warning) -> bool:
         if not issubclass(warning.category, self._warning_class):
             return False
         return all(test(warning) for test in self._tests)
 
-    def add_test(self, cb):
+    def add_test(self, cb: Callable[[Warning], bool]) -> None:
         """Add a test callback.
 
         This callback is called after determining that the right warning
diff --git a/test_asserts.py b/test_asserts.py
index d66d61b..52d505a 100644
--- a/test_asserts.py
+++ b/test_asserts.py
@@ -1269,8 +1269,9 @@ def extra_test(warning):
     def test_assert_warns__add_test_not_called(self):
         called = Box(False)
 
-        def extra_test(_):
+        def extra_test(_: Warning) -> bool:
             called.value = True
+            return False
 
         with assert_raises(AssertionError):
             with assert_warns(UserWarning) as context:
@@ -1342,10 +1343,7 @@ def test_assert_warns_regex__not_issued__default_message(self):
                 pass
 
     def test_assert_warns_regex__not_issued__custom_message(self):
-        expected = (
-            "no ImportWarning matching 'abc' issued;ImportWarning;"
-            "ImportWarning;abc"
-        )
+        expected = "no ImportWarning matching 'abc' issued;ImportWarning;ImportWarning;abc"
         with _assert_raises_assertion(expected):
             msg_fmt = "{msg};{exc_type.__name__};{exc_name};{pattern}"
             with assert_warns_regex(ImportWarning, r"abc", msg_fmt=msg_fmt):