diff --git a/Tests/helper.py b/Tests/helper.py
index 88c1f02a803..7a203eae872 100644
--- a/Tests/helper.py
+++ b/Tests/helper.py
@@ -11,6 +11,7 @@
 import sysconfig
 import tempfile
 from io import BytesIO
+from typing import Sequence, Any, Callable
 
 import pytest
 from packaging.version import parse as parse_version
@@ -28,16 +29,16 @@
 
     class test_image_results:
         @staticmethod
-        def upload(a, b):
+        def upload(a: Image.Image, b: Image.Image) -> None:
             a.show()
             b.show()
 
 elif "GITHUB_ACTIONS" in os.environ:
     HAS_UPLOADER = True
 
-    class test_image_results:
+    class test_image_results:  # type: ignore[no-redef]
         @staticmethod
-        def upload(a, b):
+        def upload(a: Image.Image, b: Image.Image) -> str:
             dir_errors = os.path.join(os.path.dirname(__file__), "errors")
             os.makedirs(dir_errors, exist_ok=True)
             tmpdir = tempfile.mkdtemp(dir=dir_errors)
@@ -47,14 +48,16 @@ def upload(a, b):
 
 else:
     try:
-        import test_image_results
+        import test_image_results  # type: ignore[import-untyped, no-redef]
 
         HAS_UPLOADER = True
     except ImportError:
         pass
 
 
-def convert_to_comparable(a, b):
+def convert_to_comparable(
+    a: Image.Image, b: Image.Image
+) -> tuple[Image.Image, Image.Image]:
     new_a, new_b = a, b
     if a.mode == "P":
         new_a = Image.new("L", a.size)
@@ -67,14 +70,16 @@ def convert_to_comparable(a, b):
     return new_a, new_b
 
 
-def assert_deep_equal(a, b, msg=None):
+def assert_deep_equal(a: Sequence, b: Sequence, msg: str | None = None) -> None:
     try:
         assert len(a) == len(b), msg or f"got length {len(a)}, expected {len(b)}"
     except Exception:
         assert a == b, msg
 
 
-def assert_image(im, mode, size, msg=None):
+def assert_image(
+    im: Image.Image, mode: str, size: tuple[int, int], msg: str | None = None
+) -> None:
     if mode is not None:
         assert im.mode == mode, (
             msg or f"got mode {repr(im.mode)}, expected {repr(mode)}"
@@ -86,7 +91,7 @@ def assert_image(im, mode, size, msg=None):
         )
 
 
-def assert_image_equal(a, b, msg=None):
+def assert_image_equal(a: Image.Image, b: Image.Image, msg: str | None = None) -> None:
     assert a.mode == b.mode, msg or f"got mode {repr(a.mode)}, expected {repr(b.mode)}"
     assert a.size == b.size, msg or f"got size {repr(a.size)}, expected {repr(b.size)}"
     if a.tobytes() != b.tobytes():
@@ -100,14 +105,18 @@ def assert_image_equal(a, b, msg=None):
         pytest.fail(msg or "got different content")
 
 
-def assert_image_equal_tofile(a, filename, msg=None, mode=None):
+def assert_image_equal_tofile(
+    a: Image.Image, filename: str, msg: str | None = None, mode: str | None = None
+) -> None:
     with Image.open(filename) as img:
         if mode:
             img = img.convert(mode)
         assert_image_equal(a, img, msg)
 
 
-def assert_image_similar(a, b, epsilon, msg=None):
+def assert_image_similar(
+    a: Image.Image, b: Image.Image, epsilon: float, msg: str | None = None
+) -> None:
     assert a.mode == b.mode, msg or f"got mode {repr(a.mode)}, expected {repr(b.mode)}"
     assert a.size == b.size, msg or f"got size {repr(a.size)}, expected {repr(b.size)}"
 
@@ -134,24 +143,32 @@ def assert_image_similar(a, b, epsilon, msg=None):
         raise e
 
 
-def assert_image_similar_tofile(a, filename, epsilon, msg=None, mode=None):
+def assert_image_similar_tofile(
+    a: Image.Image,
+    filename: str,
+    epsilon: float,
+    msg: str | None = None,
+    mode: str | None = None,
+) -> None:
     with Image.open(filename) as img:
         if mode:
             img = img.convert(mode)
         assert_image_similar(a, img, epsilon, msg)
 
 
-def assert_all_same(items, msg=None):
+def assert_all_same(items: Sequence[Any], msg: str | None = None) -> None:
     assert items.count(items[0]) == len(items), msg
 
 
-def assert_not_all_same(items, msg=None):
+def assert_not_all_same(items: Sequence[Any], msg: str | None = None) -> None:
     assert items.count(items[0]) != len(items), msg
 
 
-def assert_tuple_approx_equal(actuals, targets, threshold, msg):
+def assert_tuple_approx_equal(
+    actuals: tuple[int, ...], targets: tuple[int, ...], threshold: int, msg: str
+) -> None:
     """Tests if actuals has values within threshold from targets"""
-    value = True
+    value = 1
     for i, target in enumerate(targets):
         value *= target - threshold <= actuals[i] <= target + threshold
 
@@ -163,17 +180,24 @@ def skip_unless_feature(feature: str) -> pytest.MarkDecorator:
     return pytest.mark.skipif(not features.check(feature), reason=reason)
 
 
-def skip_unless_feature_version(feature, version_required, reason=None):
+def skip_unless_feature_version(
+    feature: str, version_required: str, reason: str | None = None
+) -> pytest.MarkDecorator:
     if not features.check(feature):
         return pytest.mark.skip(f"{feature} not available")
     if reason is None:
         reason = f"{feature} is older than {version_required}"
-    version_required = parse_version(version_required)
+    version_required_ = parse_version(version_required)
     version_available = parse_version(features.version(feature))
-    return pytest.mark.skipif(version_available < version_required, reason=reason)
+    return pytest.mark.skipif(version_available < version_required_, reason=reason)
 
 
-def mark_if_feature_version(mark, feature, version_blacklist, reason=None):
+def mark_if_feature_version(
+    mark: pytest.MarkDecorator,
+    feature: str,
+    version_blacklist: str,
+    reason: str | None = None,
+) -> pytest.MarkDecorator:
     if not features.check(feature):
         return pytest.mark.pil_noop_mark()
     if reason is None:
@@ -194,7 +218,7 @@ class PillowLeakTestCase:
     iterations = 100  # count
     mem_limit = 512  # k
 
-    def _get_mem_usage(self):
+    def _get_mem_usage(self) -> float:
         """
         Gets the RUSAGE memory usage, returns in K. Encapsulates the difference
         between macOS and Linux rss reporting
@@ -216,7 +240,7 @@ def _get_mem_usage(self):
         #  This is the maximum resident set size used (in kilobytes).
         return mem  # Kb
 
-    def _test_leak(self, core):
+    def _test_leak(self, core: Callable[[], None]) -> None:
         start_mem = self._get_mem_usage()
         for cycle in range(self.iterations):
             core()
@@ -228,17 +252,22 @@ def _test_leak(self, core):
 # helpers
 
 
-def fromstring(data):
+def fromstring(data: bytes) -> Image.Image:
     return Image.open(BytesIO(data))
 
 
-def tostring(im, string_format, **options):
+def tostring(im: Image.Image, string_format: str, **options: Any) -> bytes:
     out = BytesIO()
     im.save(out, string_format, **options)
     return out.getvalue()
 
 
-def hopper(mode=None, cache={}):
+def hopper(
+    mode: str | None = None, cache: dict[str, Image.Image] | None = None
+) -> Image.Image:
+    if cache is None:
+        cache = {}
+
     if mode is None:
         # Always return fresh not-yet-loaded version of image.
         # Operations on not-yet-loaded images is separate class of errors
@@ -259,29 +288,31 @@ def hopper(mode=None, cache={}):
     return im.copy()
 
 
-def djpeg_available():
+def djpeg_available() -> bool:
     if shutil.which("djpeg"):
         try:
             subprocess.check_call(["djpeg", "-version"])
             return True
         except subprocess.CalledProcessError:  # pragma: no cover
             return False
+    return False
 
 
-def cjpeg_available():
+def cjpeg_available() -> bool:
     if shutil.which("cjpeg"):
         try:
             subprocess.check_call(["cjpeg", "-version"])
             return True
         except subprocess.CalledProcessError:  # pragma: no cover
             return False
+    return False
 
 
-def netpbm_available():
+def netpbm_available() -> bool:
     return bool(shutil.which("ppmquant") and shutil.which("ppmtogif"))
 
 
-def magick_command():
+def magick_command() -> list[str] | None:
     if sys.platform == "win32":
         magickhome = os.environ.get("MAGICK_HOME")
         if magickhome:
@@ -299,46 +330,48 @@ def magick_command():
     if graphicsmagick and shutil.which(graphicsmagick[0]):
         return graphicsmagick
 
+    return None
+
 
-def on_appveyor():
+def on_appveyor() -> bool:
     return "APPVEYOR" in os.environ
 
 
-def on_github_actions():
+def on_github_actions() -> bool:
     return "GITHUB_ACTIONS" in os.environ
 
 
-def on_ci():
+def on_ci() -> bool:
     # GitHub Actions and AppVeyor have "CI"
     return "CI" in os.environ
 
 
-def is_big_endian():
+def is_big_endian() -> bool:
     return sys.byteorder == "big"
 
 
-def is_ppc64le():
+def is_ppc64le() -> bool:
     import platform
 
     return platform.machine() == "ppc64le"
 
 
-def is_win32():
+def is_win32() -> bool:
     return sys.platform.startswith("win32")
 
 
-def is_pypy():
+def is_pypy() -> bool:
     return hasattr(sys, "pypy_translation_info")
 
 
-def is_mingw():
+def is_mingw() -> bool:
     return sysconfig.get_platform() == "mingw"
 
 
 class CachedProperty:
-    def __init__(self, func):
+    def __init__(self, func: Callable[[Any], Any]) -> None:
         self.func = func
 
-    def __get__(self, instance, cls=None):
+    def __get__(self, instance: dict[Any, Callable[[], Any]], cls: Any = None) -> Any:
         result = instance.__dict__[self.func.__name__] = self.func(instance)
         return result