diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 8d11a60..1035e73 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -24,9 +24,16 @@ concurrency:
   cancel-in-progress: true
 
 jobs:
+  ruff:
+    runs-on: ubuntu-latest
+    timeout-minutes: &timeout-minutes 5
+    steps:
+      - uses: actions/checkout@v6
+      - uses: astral-sh/ruff-action@v4.0.0
+
   mypy:
     runs-on: ${{ matrix.os }}
-    timeout-minutes: &timeout-minutes 5
+    timeout-minutes: *timeout-minutes
     strategy:
       # mypy is os and python-version sensitive. Test on all supported combinations
       matrix:
@@ -42,3 +49,59 @@ jobs:
           activate-environment: true
       - run: uv sync --locked
       - run: mypy . --python-version=${{ matrix.python-version }}
+
+  tests:
+    runs-on: ${{ matrix.os }}
+    timeout-minutes: *timeout-minutes
+    strategy:
+      # Test on all supported runtime combinations
+      matrix:
+        # Arm runners are faster (as long as the same wheels are available)
+        # This project doesn't have any code that should act differently per architecture
+        os: [windows-11-arm, ubuntu-24.04-arm, macos-latest]
+        # TODO: Run tests in parallel on free-threaded python to catch free-threading issues
+        # See: https://py-free-threading.github.io/testing/
+        python-version: ["3.9", "3.10", "3.11", "3.12", "3.13", "3.14"]
+      fail-fast: false
+    steps:
+      - uses: actions/checkout@v6
+      - name: Install Linux Packages
+        if: ${{ startsWith(matrix.os, 'ubuntu') }}
+        run: |
+          sudo apt update
+          # xvfb+openbox: headless X server and WM
+          # gedit: the test window (not preinstalled on GitHub runners)
+          # x11-xserver-utils (xrandr/xset): required by tests for window geometry
+          # dbus-x11: dbus-launch, so the GTK app (gedit) gets a session bus
+          sudo apt install -y xvfb openbox gedit x11-xserver-utils dbus-x11
+      - uses: astral-sh/setup-uv@v8.2.0
+        with:
+          python-version: ${{ matrix.python-version }}
+          activate-environment: true
+      - run: uv sync --locked
+      - name: Run tests (Linux)
+        if: ${{ startsWith(matrix.os, 'ubuntu') }}
+        working-directory: tests
+        run: xvfb-run --server-args="-screen 0 1280x1024x24" bash -c "openbox & sleep 1 && dbus-launch --exit-with-session python test_pywinbox.py"
+      - name: Run tests (Windows & macOS)
+        if: ${{ !startsWith(matrix.os, 'ubuntu') }}
+        working-directory: tests
+        run: python test_pywinbox.py
+      - name: Run tests (MacNSBox)
+        if: ${{ startsWith(matrix.os, 'macos') }}
+        working-directory: tests
+        run: python test_MacNSBox.py
+
+  sphinx:
+    runs-on: ubuntu-24.04-arm # Keep in sync with build.os in .readthedocs.yaml
+    timeout-minutes: *timeout-minutes
+    steps:
+      - uses: actions/checkout@v6
+      - uses: astral-sh/setup-uv@v8.2.0
+        with:
+          python-version: "3.14" # Keep in sync with build.tools.python in .readthedocs.yaml
+          activate-environment: true
+      - run: uv sync --locked --no-default-groups --group=docs
+      - name: Build docs
+        # TODO: Add --fail-on-warning, but still too many warnings right now
+        run: sphinx-build --keep-going --builder html docs/source docs/_build/html
diff --git a/pyproject.toml b/pyproject.toml
index ae61319..a507024 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -71,6 +71,7 @@ dependencies = [
 docs = ["myst-parser"]
 dev = [
     { include-group = "docs" },
+    "ruff>=0.15.16",
     "ewmhlib",
     "pywinctl>=0.3",
     "mypy>=0.990,<2",
diff --git a/ruff.toml b/ruff.toml
new file mode 100644
index 0000000..f97e36a
--- /dev/null
+++ b/ruff.toml
@@ -0,0 +1,90 @@
+[lint]
+future-annotations = true
+# https://docs.astral.sh/ruff/rules/
+extend-select = [
+  "ANN2", # flake8-annotations: missing-return-type
+  "C4", # flake8-comprehensions
+  "F401", # unused-import
+  "F404", # late-future-import
+  "FA", # flake8-future-annotations
+  "FLY", # Flynt
+  "ICN", # flake8-import-conventions
+  "PERF", # Perflint
+  "PGH", # pygrep-hooks (blanket-* rules)
+  "PYI", # flake8-pyi
+  "RUF", # Ruff-specific rules
+  "SIM9", # flake8-simplify: split-static-string + zip-dict-keys-and-values
+  "SLOT", # flake8-slots
+  "TC", # flake8-type-checking
+  "TID", # flake8-tidy-imports
+  "UP", # pyupgrade
+  "YTT", # flake8-2020
+]
+ignore = [
+  # Only enforce return types on public functions. Where otherwise mypy infers as Any
+  # Still worth running `ruff check --fix --select=202` once in a while for autofixes
+  "ANN202", # missing-return-type-private-function
+  # Explicit is preferred
+  "UP015", # redundant-open-modes, 
+  # Autofixes print-f style formatting to f-strings,
+  # which is sometimes simpler, but looses template code reading semantics
+  "UP032", # f-string
+  # TC helps prevent circular imports, reduce runtime cost of typing symbols,
+  # and prevent leaking implementations details into modules
+  # However stdlib is not at risk of circular import, is clearly not public API,
+  # and assume it's gonna be included in the import chain at some point anyway
+  "TC003", # typing-only-standard-library-import
+  # Typeshed doesn't want complex or non-literal defaults for maintenance and testing reasons.
+  # This doesn't affect us, let's have more complete stubs.
+  "PYI011", # typed-argument-default-in-stub
+  "PYI014", # argument-default-in-stub
+  "PYI053", # string-or-bytes-too-long
+  # Good to watch for, but often unfixable
+  # Anyway Python 3.11 introduced "zero cost" exception handling
+  "PERF203", # try-except-in-loop,
+
+  # TODO: Add and configure isort (I) first
+  "RUF022",
+
+  # TODO: Consider later
+  "UP031", # printf-string-formatting
+  "RUF059", # unused-unpacked-variable
+
+  # TODO: Not autofixable, address in a separate PR !
+  "E402",
+  "E722",
+  "PYI063",
+]
+# F401 would remove imports not marked as explicit re-exports, which may break API boundaries
+extend-unsafe-fixes = ["F401"]
+
+[lint.per-file-ignores]
+"**/typings/**/*.pyi" = [
+  "E402", # https://github.com/astral-sh/ruff/issues/26160
+  "F811", # Re-exports false positives
+  # The following can't be controlled for external libraries:
+  "A", # Shadowing builtin names
+  "E741", # ambiguous variable name
+  "F403", # `from . import *` used; unable to detect undefined names
+  "FBT", # flake8-boolean-trap
+  "ICN001", # unconventional-import-alias
+  "N8", # Naming conventions
+  "PLC2701", # Private name import
+  "PLE0302", # The special method expects a given signature
+  "PLR0904", # Too many public methods
+  "PLR0913", # Argument count
+  "PLR0917", # Too many positional arguments
+  "PLW3201", # misspelled dunder method name
+  "SLOT", # flake8-slots
+  # Stubs can sometimes re-export entire modules.
+  # Issues with using a star-imported name will be caught by type-checkers.
+  "F405", # may be undefined, or defined from star imports
+  # It's normal to be missing annotations for local stubs.
+  # If they were complete, we'd upload them to typeshed!
+  "ANN0",
+  "ANN2",
+]
+
+# https://docs.astral.sh/ruff/settings/#lintflake8-type-checking
+[lint.flake8-type-checking]
+quote-annotations = true
diff --git a/src/pywinbox/__init__.py b/src/pywinbox/__init__.py
index 10dd9c6..464732f 100644
--- a/src/pywinbox/__init__.py
+++ b/src/pywinbox/__init__.py
@@ -1,5 +1,4 @@
 #!/usr/bin/python
-# -*- coding: utf-8 -*-
 from importlib.metadata import version as _importlib_version
 
 __all__ = [
diff --git a/src/pywinbox/_main.py b/src/pywinbox/_main.py
index 2c853ca..42a475b 100644
--- a/src/pywinbox/_main.py
+++ b/src/pywinbox/_main.py
@@ -1,10 +1,9 @@
 #!/usr/bin/python
-# -*- coding: utf-8 -*-
 from __future__ import annotations
 
 import sys
 from collections.abc import Callable
-from typing import Union, Tuple, NamedTuple, Optional
+from typing import NamedTuple
 
 class Box(NamedTuple):
     """Container class to handle Box struct (left, top, width, height)"""
@@ -41,7 +40,7 @@ def pointInBox(x: int, y: int, box: Box) -> bool:
 
 class PyWinBox:
 
-    def __init__(self, onQuery: Optional[Callable[[], Box]] = None, onSet: Optional[Callable[[Box], None]] = None, handle=None):
+    def __init__(self, onQuery: Callable[[], Box] | None = None, onSet: Callable[[Box], None] | None = None, handle=None) -> None:
         """
         Class to access all area/window box properties.
 
@@ -111,7 +110,7 @@ def onSet(self, newBox: Box):
         if self._handle is not None:
             _moveResizeWindow(self._handle, newBox)
 
-    def __repr__(self):
+    def __repr__(self) -> str:
         """Return a string of the constructor function call to create this Box object."""
         return "%s(left=%s, top=%s, width=%s, height=%s)" % (
             self.__class__.__name__,
@@ -121,7 +120,7 @@ def __repr__(self):
             self._box.height,
         )
 
-    def __str__(self):
+    def __str__(self) -> str:
         """Return a string representation of this Box object."""
         return "(%s, %s, %s, %s)" % (
             self._box.left,
@@ -202,7 +201,7 @@ def position(self) -> Point:
         return Point(self._box.left, self._box.top)
 
     @position.setter
-    def position(self, value: Union[Point, Tuple[int, int]]):
+    def position(self, value: Point | tuple[int, int]):
         val: Point = Point(*value)
         self._box = self._onQuery()
         self._box = Box(val.x, val.y, self._box.width, self._box.height)
@@ -214,7 +213,7 @@ def size(self) -> Size:
         return Size(self._box.width, self._box.height)
 
     @size.setter
-    def size(self, value: Union[Size, Tuple[int, int]]):
+    def size(self, value: Size | tuple[int, int]):
         val: Size = Size(*value)
         self._box = self._onQuery()
         self._box = Box(self._box.left, self._box.top, val.width, val.height)
@@ -226,7 +225,7 @@ def box(self) -> Box:
         return self._box
 
     @box.setter
-    def box(self, value: Union[Box, Tuple[int, int, int, int]]):
+    def box(self, value: Box | tuple[int, int, int, int]):
         val: Box = Box(*value)
         self._box = val
         self._onSet(self._box)
@@ -238,7 +237,7 @@ def rect(self) -> Rect:
                     self._box.top + self._box.height)
 
     @rect.setter
-    def rect(self, value: Union[Rect, Tuple[int, int, int, int]]):
+    def rect(self, value: Rect | tuple[int, int, int, int]):
         val: Rect = Rect(*value)
         self._box = Box(val.left, val.top, abs(val.right - val.left), abs(val.bottom - val.top))
         self._onSet(self._box)
@@ -249,7 +248,7 @@ def topleft(self) -> Point:
         return Point(self._box.left, self._box.top)
 
     @topleft.setter
-    def topleft(self, value: Union[Point, Tuple[int, int]]):
+    def topleft(self, value: Point | tuple[int, int]):
         val: Point = Point(*value)
         self._box = self._onQuery()
         self._box = Box(val.x, val.y, self._box.width, self._box.height)
@@ -261,7 +260,7 @@ def bottomleft(self) -> Point:
         return Point(self._box.left, self._box.top + self._box.height)
 
     @bottomleft.setter
-    def bottomleft(self, value: Union[Point, Tuple[int, int]]):
+    def bottomleft(self, value: Point | tuple[int, int]):
         val: Point = Point(*value)
         self._box = self._onQuery()
         self._box = Box(val.x, val.y - self._box.height, self._box.width, self._box.height)
@@ -273,7 +272,7 @@ def topright(self) -> Point:
         return Point(self._box.left + self._box.width, self._box.top)
 
     @topright.setter
-    def topright(self, value: Union[Point, Tuple[int, int]]):
+    def topright(self, value: Point | tuple[int, int]):
         val: Point = Point(*value)
         self._box = self._onQuery()
         self._box = Box(val.x - self._box.width, val.y, self._box.width, self._box.height)
@@ -285,7 +284,7 @@ def bottomright(self) -> Point:
         return Point(self._box.left + self._box.width, self._box.top + self._box.height)
 
     @bottomright.setter
-    def bottomright(self, value: Union[Point, Tuple[int, int]]):
+    def bottomright(self, value: Point | tuple[int, int]):
         val: Point = Point(*value)
         self._box = self._onQuery()
         self._box = Box(val.x - self._box.width, val.y - self._box.height, self._box.width, self._box.height)
@@ -297,7 +296,7 @@ def midtop(self) -> Point:
         return Point(self._box.left + (self._box.width // 2), self._box.top)
 
     @midtop.setter
-    def midtop(self, value: Union[Point, Tuple[int, int]]):
+    def midtop(self, value: Point | tuple[int, int]):
         val: Point = Point(*value)
         self._box = self._onQuery()
         self._box = Box(val.x - (self._box.width // 2), val.y, self._box.width, self._box.height)
@@ -309,7 +308,7 @@ def midbottom(self) -> Point:
         return Point(self._box.left + (self._box.width // 2), self._box.top + self._box.height)
 
     @midbottom.setter
-    def midbottom(self, value: Union[Point, Tuple[int, int]]):
+    def midbottom(self, value: Point | tuple[int, int]):
         val: Point = Point(*value)
         self._box = self._onQuery()
         self._box = Box(val.x - (self._box.width // 2), val.y - self._box.height, self._box.width, self._box.height)
@@ -321,7 +320,7 @@ def midleft(self) -> Point:
         return Point(self._box.left, self._box.top + (self._box.height // 2))
 
     @midleft.setter
-    def midleft(self, value: Union[Point, Tuple[int, int]]):
+    def midleft(self, value: Point | tuple[int, int]):
         val: Point = Point(*value)
         self._box = self._onQuery()
         self._box = Box(val.x, val.y - (self._box.height // 2), self._box.width, self._box.height)
@@ -333,7 +332,7 @@ def midright(self) -> Point:
         return Point(self._box.left + self._box.width, self._box.top + (self._box.height // 2))
 
     @midright.setter
-    def midright(self, value: Union[Point, Tuple[int, int]]):
+    def midright(self, value: Point | tuple[int, int]):
         val: Point = Point(*value)
         self._box = self._onQuery()
         self._box = Box(val.x - self._box.width, val.y - (self._box.height // 2), self._box.width, self._box.height)
@@ -345,7 +344,7 @@ def center(self) -> Point:
         return Point(self._box.left + (self._box.width // 2), self._box.top + (self._box.height // 2))
 
     @center.setter
-    def center(self, value: Union[Point, Tuple[int, int]]):
+    def center(self, value: Point | tuple[int, int]):
         val: Point = Point(*value)
         self._box = self._onQuery()
         self._box = Box(val.x - (self._box.width // 2), val.y - (self._box.height // 2), self._box.width, self._box.height)
diff --git a/src/pywinbox/_pywinbox_linux.py b/src/pywinbox/_pywinbox_linux.py
index 4f10e59..bc5f183 100644
--- a/src/pywinbox/_pywinbox_linux.py
+++ b/src/pywinbox/_pywinbox_linux.py
@@ -1,12 +1,10 @@
 #!/usr/bin/python
-# -*- coding: utf-8 -*-
 from __future__ import annotations
 
 import os
 import sys
 assert sys.platform == "linux"
 
-from typing import Union, Optional
 
 from Xlib.xobject.drawable import Window as XWindow
 
@@ -14,7 +12,7 @@
 from ewmhlib import EwmhWindow
 
 
-def _getHandle(handle: Union[int, XWindow]) -> Optional[EwmhWindow]:
+def _getHandle(handle: int | XWindow) -> EwmhWindow | None:
 
     newHandle = None
     if isinstance(handle, int):
diff --git a/src/pywinbox/_pywinbox_macos.py b/src/pywinbox/_pywinbox_macos.py
index 5bb81dc..a9c6c60 100644
--- a/src/pywinbox/_pywinbox_macos.py
+++ b/src/pywinbox/_pywinbox_macos.py
@@ -1,5 +1,4 @@
 #!/usr/bin/python
-# -*- coding: utf-8 -*-
 # Incomplete type stubs for pyobjc
 # mypy: disable_error_code = no-any-return
 from __future__ import annotations
@@ -9,7 +8,7 @@
 assert sys.platform == "darwin"
 
 import subprocess
-from typing import NamedTuple, Union, Optional, cast
+from typing import NamedTuple, cast
 
 import AppKit
 
@@ -27,7 +26,7 @@ class _macOSCGHandle(NamedTuple):
     windowTitle: str
 
 
-def _getHandle(handle) -> Optional[Union[_macOSCGHandle, _macOSNSHandle]]:
+def _getHandle(handle) -> _macOSCGHandle | _macOSNSHandle | None:
     newHandle = None
     if isinstance(handle, tuple):
         app, window = handle
@@ -71,21 +70,21 @@ def _checkPermissions(activate: bool = False) -> bool:
     return ret == "true"
 
 
-def _getWindowBox(handle: Union[_macOSNSHandle, _macOSCGHandle], flipValues: bool = False):
+def _getWindowBox(handle: _macOSNSHandle | _macOSCGHandle, flipValues: bool = False):
     if handle.isNSHandle:
-        handle = cast(_macOSNSHandle, handle)
+        handle = cast("_macOSNSHandle", handle)
         return _NSgetWindowBox(handle.window, flipValues)
     else:
-        handle = cast(_macOSCGHandle, handle)
+        handle = cast("_macOSCGHandle", handle)
         return _CGgetWindowBox(handle.appName, handle.windowTitle)
 
 
-def _moveResizeWindow(handle: Union[_macOSNSHandle, _macOSCGHandle], newBox: Box, flipValues: bool = False):
+def _moveResizeWindow(handle: _macOSNSHandle | _macOSCGHandle, newBox: Box, flipValues: bool = False):
     if handle.isNSHandle:
-        handle = cast(_macOSNSHandle, handle)
+        handle = cast("_macOSNSHandle", handle)
         _NSmoveResizeTo(handle.window, newBox, flipValues)
     else:
-        handle = cast(_macOSCGHandle, handle)
+        handle = cast("_macOSCGHandle", handle)
         _CGmoveResizeTo(handle.appName, handle.windowTitle, newBox)
 
 
diff --git a/src/pywinbox/_pywinbox_win.py b/src/pywinbox/_pywinbox_win.py
index ce201c1..02f2e4e 100644
--- a/src/pywinbox/_pywinbox_win.py
+++ b/src/pywinbox/_pywinbox_win.py
@@ -1,12 +1,10 @@
 #!/usr/bin/python
-# -*- coding: utf-8 -*-
 from __future__ import annotations
 
 import sys
 
 assert sys.platform == "win32"
 
-from typing import Union, Optional
 
 import ctypes
 import win32gui
@@ -25,7 +23,7 @@
     ctypes.windll.shcore.SetProcessDpiAwareness(1)
 
 
-def _getHandle(handle: Union[int, str]) -> Optional[int]:
+def _getHandle(handle: int | str) -> int | None:
     newHandle = None
     if isinstance(handle, str):
         try:
diff --git a/tests/test_MacNSBox.py b/tests/test_MacNSBox.py
index 7ca71ae..cefc4d8 100644
--- a/tests/test_MacNSBox.py
+++ b/tests/test_MacNSBox.py
@@ -1,15 +1,15 @@
 #!/usr/bin/env python
-# encoding: utf-8
 
 # Lawrence Akka - https://sourceforge.net/p/pyobjc/mailman/pyobjc-dev/thread/0B4BC391-6491-445D-92D0-7B1CEF6F51BE%40me.com/#msg27726282
 
 # We need to import the relevant object definitions from PyObjC
 
+import os
 import sys
+import traceback
 
 import pywinbox
 
-assert sys.platform == "darwin"
 
 import time
 
@@ -25,11 +25,25 @@ class Delegate(NSObject):
 
     npw = None
 
-    def applicationSupportsSecureRestorableState_(self, app):
+    def applicationSupportsSecureRestorableState_(self, app) -> bool:
         return True
 
-    def applicationDidFinishLaunching_(self, aNotification: None):
+    def applicationDidFinishLaunching_(self, aNotification: None) -> None:
         '''Called automatically when the application has launched'''
+        # PyObjC swallows exceptions raised inside delegate callbacks (only logging the type),
+        # so the window would never close and the app would hang forever.
+        # Catch everything, print the traceback, and force-exit nonzero so the test fails fast.
+        # We can't use NSApp().terminate_() (it exits 0) nor sys.exit() (SystemExit isn't an
+        # Exception subclass, so PyObjC swallows it too): os._exit() is the only reliable path.
+        try:
+            self._runChecks()
+        except Exception:
+            traceback.print_exc()
+            sys.stdout.flush()
+            sys.stderr.flush()
+            os._exit(1)
+
+    def _runChecks(self) -> None:
         # Set it as the frontmost application
         NSApp().activateIgnoringOtherApps_(True)
 
@@ -38,9 +52,18 @@ def applicationDidFinishLaunching_(self, aNotification: None):
             handle = win
             print(win.title(), win.frame(), type(win.frame().origin))
         print()
+        assert handle is not None
 
         myPyBox = pywinbox.PyWinBox(onQuery=None, onSet=None, handle=handle)
 
+        # macOS won't let a window's top edge rise above the menu bar, so any
+        # target whose top edge exceeds the usable screen height gets clamped.
+        # CI runners have a small headless display, so derive bottom targets
+        # from the actual screen height instead of assuming a tall desktop.
+        screenH = int(handle.screen().frame().size.height)
+        print("SCREEN", handle.screen().frame())
+        lowBottom = min(700, screenH - 100)
+
         timelap = 0.3
 
         print("MOVE left = 200", myPyBox.box, myPyBox.rect)
@@ -58,10 +81,10 @@ def applicationDidFinishLaunching_(self, aNotification: None):
         time.sleep(timelap)
         assert myPyBox.top == 200
 
-        print("MOVE bottom = 800", myPyBox.box, myPyBox.rect)
-        myPyBox.bottom = 800
+        print(f"MOVE bottom = {lowBottom}", myPyBox.box, myPyBox.rect)
+        myPyBox.bottom = lowBottom
         time.sleep(timelap)
-        assert myPyBox.bottom == 800
+        assert myPyBox.bottom == lowBottom
 
         print("MOVE topleft = (300, 400)", myPyBox.box, myPyBox.rect)
         myPyBox.topleft = (300, 400)
@@ -73,10 +96,10 @@ def applicationDidFinishLaunching_(self, aNotification: None):
         time.sleep(timelap)
         assert myPyBox.topright == (300, 400)
 
-        print("MOVE bottomleft = (300, 700)", myPyBox.box, myPyBox.rect)
-        myPyBox.bottomleft = (300, 700)
+        print(f"MOVE bottomleft = (300, {lowBottom})", myPyBox.box, myPyBox.rect)
+        myPyBox.bottomleft = (300, lowBottom)
         time.sleep(timelap)
-        assert myPyBox.bottomleft == (300, 700)
+        assert myPyBox.bottomleft == (300, lowBottom)
 
         print("MOVE bottomright = (1000, 200)", myPyBox.box, myPyBox.rect)
         myPyBox.bottomright = (1000, 200)
@@ -98,10 +121,10 @@ def applicationDidFinishLaunching_(self, aNotification: None):
         time.sleep(timelap)
         assert myPyBox.midtop == (300, 400)
 
-        print("MOVE midbottom = (300, 700)", myPyBox.box, myPyBox.rect)
-        myPyBox.midbottom = (300, 700)
+        print(f"MOVE midbottom = (300, {lowBottom})", myPyBox.box, myPyBox.rect)
+        myPyBox.midbottom = (300, lowBottom)
         time.sleep(timelap)
-        assert myPyBox.midbottom == (300, 700)
+        assert myPyBox.midbottom == (300, lowBottom)
 
         print("MOVE center = (300, 400)", myPyBox.box, myPyBox.rect)
         myPyBox.center = (300, 400)
@@ -137,23 +160,23 @@ def applicationDidFinishLaunching_(self, aNotification: None):
         print("CLOSE")
         win.close()
 
-    def windowWillClose_(self, aNotification: None):
+    def windowWillClose_(self, aNotification: None) -> None:
         '''Called automatically when the window is closed'''
         print("Window has been closed")
         # Terminate the application
         NSApp().terminate_(self)
 
-    def windowDidBecomeKey_(self, aNotification: None):
+    def windowDidBecomeKey_(self, aNotification: None) -> None:
         print("Now I'm ACTIVE")
 
 
-def demo():
+def demo() -> None:
     # Create a new application instance ...
     a = NSApplication.sharedApplication()
     # ... and create its delegate.  Note the use of the
     # Objective C constructors below, because Delegate
     # is a subclass of an Objective C class, NSObject
-    delegate = Delegate.alloc().init()
+    delegate: Delegate = Delegate.alloc().init()
     # Tell the application which delegate object to use.
     a.setDelegate_(delegate)
 
@@ -168,11 +191,14 @@ def demo():
     # to be the same delegate as the application is using)...
     w.setDelegate_(delegate)
     # ... and set some properties. Unicode strings are preferred.
-    w.setTitle_(u'Hello, World!')
+    w.setTitle_('Hello, World!')
     # All set. Now we can show the window ...
     w.orderFrontRegardless()
 
     # ... and start the application
+    # On success the window closes -> windowWillClose_ -> terminate_ (exits 0).
+    # On failure _runChecks' handler calls os._exit(1). Either way control does not
+    # return here, so there's nothing to do after a.run().
     a.run()
     #AppHelper.runEventLoop()
 
diff --git a/tests/test_pywinbox.py b/tests/test_pywinbox.py
index e31f084..a446764 100644
--- a/tests/test_pywinbox.py
+++ b/tests/test_pywinbox.py
@@ -1,158 +1,172 @@
 #!/usr/bin/python
-# -*- coding: utf-8 -*-
 
 from __future__ import annotations
 
+import os
 import subprocess
 import sys
 import time
+from typing import TypedDict
 
-import pywinbox
 import pywinctl
 
+import pywinbox
 
-def test_basic():
-
-    npw = None
 
-    if sys.platform == "win32":
-        subprocess.Popen('notepad')
-        time.sleep(0.5)
+class GetWindowKwargs(TypedDict):
+    title: str
+    condition: int  # TODO: Consider making pywinctl.Re an IntEnum
 
-        npw = pywinctl.getActiveWindow()
 
+def test_basic() -> None:
+    if sys.platform == "win32":
+        process = "notepad"
+        get_window_kwargs: GetWindowKwargs = {
+            "title": "Notepad",
+            "condition": pywinctl.Re.ENDSWITH,
+        }
     elif sys.platform == "linux":
-        subprocess.Popen('gedit')
-        time.sleep(5)
-
-        npw = pywinctl.getActiveWindow()
-
+        process = "gedit"
+        get_window_kwargs: GetWindowKwargs = {
+            "title": "gedit",
+            "condition": pywinctl.Re.ENDSWITH,
+        }
     elif sys.platform == "darwin":
         if not pywinctl.checkPermissions(activate=True):
             exit()
-        subprocess.Popen(['touch', 'test.py'])
-        time.sleep(2)
-        subprocess.Popen(['open', '-a', 'TextEdit', 'test.py'])
-        time.sleep(5)
-
-        windows = pywinctl.getWindowsWithTitle('test.py')
-        if windows:
-            npw = windows[0]
-
-    if npw is not None:
-
-        wait = True
-        timelap = 0.5
-
-        # Test maximize/minimize/restore.
-        if npw.isMaximized:  # Make sure it starts un-maximized
-            npw.restore(wait=wait)
-        assert not npw.isMaximized
-        
-        npw.size = (600, 400)
-
-        if sys.platform == "darwin":
-            myPyBox = pywinbox.PyWinBox(onQuery=None, onSet=None, handle=(npw.getAppName(), npw.title or ""))
-        else:
-            myPyBox = pywinbox.PyWinBox(onQuery=None, onSet=None, handle=npw.getHandle())
-
-        print("INIT", npw.box, npw.rect)
-
-        myPyBox.left = 250
-        time.sleep(timelap)
-        print("LEFT", npw.box, npw.rect)
-        assert npw.left == 250
-
-        myPyBox.right = 950
-        time.sleep(timelap)
-        print("RIGHT", npw.box, npw.rect)
-        assert npw.right == 950
-
-        myPyBox.top = 150
-        time.sleep(timelap)
-        print("TOP", npw.box, npw.rect)
-        assert npw.top == 150
-
-        myPyBox.bottom = 775
-        time.sleep(timelap)
-        print("BOTTOM", npw.box, npw.rect)
-        assert npw.bottom == 775
-
-        myPyBox.topleft = (155, 350)
-        time.sleep(timelap)
-        print(npw.box, npw.rect)
-        assert npw.topleft == (155, 350)
-
-        myPyBox.topright = (1000, 300)
-        time.sleep(timelap)
-        print(npw.box, npw.rect)
-        assert npw.topright == (1000, 300)
-
-        myPyBox.bottomleft = (300, 975)
-        time.sleep(timelap)
-        print(npw.box, npw.rect)
-        assert npw.bottomleft == (300, 975)
-
-        myPyBox.bottomright = (1000, 900)
-        time.sleep(timelap)
-        print(npw.box, npw.rect)
-        assert npw.bottomright == (1000, 900)
-
-        myPyBox.midleft = (300, 400)
-        time.sleep(timelap)
-        print(npw.box, npw.rect)
-        assert npw.midleft == (300, 400)
-
-        myPyBox.midright = (1050, 600)
-        time.sleep(timelap)
-        print(npw.box, npw.rect)
-        assert npw.midright == (1050, 600)
-
-        myPyBox.midtop = (500, 350)
-        time.sleep(timelap)
-        print(npw.box, npw.rect)
-        assert npw.midtop == (500, 350)
-
-        myPyBox.midbottom = (500, 800)
-        time.sleep(timelap)
-        print(npw.box, npw.rect)
-        assert npw.midbottom == (500, 800)
-
-        myPyBox.center = (500, 350)
-        time.sleep(timelap)
-        print(npw.box, npw.rect)
-        assert npw.center == (500, 350)
-
-        myPyBox.centerx = 1000
-        time.sleep(timelap)
-        print(npw.box, npw.rect)
-        assert npw.centerx == 1000
-
-        myPyBox.centery = 600
-        time.sleep(timelap)
-        print(npw.box, npw.rect)
-        assert npw.centery == 600
-
-        myPyBox.width = 700
-        time.sleep(timelap)
-        print(npw.box, npw.rect)
-        assert npw.width == 700
-
-        myPyBox.height = 400
-        time.sleep(timelap)
-        print(npw.box, npw.rect)
-        assert npw.height == 400
-
-        myPyBox.size = (551, 401)
-        time.sleep(timelap)
-        print(npw.box, npw.rect)
-        assert npw.size == (551, 401)
-
-        # Test closing
-        npw.close()
-
-
-def main():
+        process = ["open", "-a", "TextEdit", __file__]
+        get_window_kwargs: GetWindowKwargs = {
+            "title": os.path.basename(__file__),
+            "condition": pywinctl.Re.IS,
+        }
+    else:
+        raise NotImplementedError(
+            "PyWinCtl currently does not support this platform. "
+            + "If you have useful knowledge, please contribute! https://github.com/Kalmat/PyWinCtl"
+        )
+
+    subprocess.Popen(process)
+
+    testWindows: list[pywinctl.Window] = []
+    deadline = time.time() + 15
+    while not testWindows and time.time() < deadline:
+        time.sleep(0.5)
+        testWindows = pywinctl.getWindowsWithTitle(**get_window_kwargs)
+    assert len(testWindows) == 1
+
+    npw = testWindows[0]
+    wait = True
+    timelap = 0.5
+
+    # Test maximize/minimize/restore.
+    if npw.isMaximized:  # Make sure it starts un-maximized
+        npw.restore(wait=wait)
+    assert not npw.isMaximized
+    
+    npw.size = (600, 400)
+
+    if sys.platform == "darwin":
+        myPyBox = pywinbox.PyWinBox(onQuery=None, onSet=None, handle=(npw.getAppName(), npw.title or ""))
+    else:
+        myPyBox = pywinbox.PyWinBox(onQuery=None, onSet=None, handle=npw.getHandle())
+
+    print("INIT", npw.box, npw.rect)
+
+    myPyBox.left = 250
+    time.sleep(timelap)
+    print("LEFT", npw.box, npw.rect)
+    assert npw.left == 250
+
+    myPyBox.right = 950
+    time.sleep(timelap)
+    print("RIGHT", npw.box, npw.rect)
+    assert npw.right == 950
+
+    myPyBox.top = 150
+    time.sleep(timelap)
+    print("TOP", npw.box, npw.rect)
+    assert npw.top == 150
+
+    myPyBox.bottom = 775
+    time.sleep(timelap)
+    print("BOTTOM", npw.box, npw.rect)
+    assert npw.bottom == 775
+
+    myPyBox.topleft = (155, 350)
+    time.sleep(timelap)
+    print(npw.box, npw.rect)
+    assert npw.topleft == (155, 350)
+
+    myPyBox.topright = (1000, 300)
+    time.sleep(timelap)
+    print(npw.box, npw.rect)
+    assert npw.topright == (1000, 300)
+
+    myPyBox.bottomleft = (300, 975)
+    time.sleep(timelap)
+    print(npw.box, npw.rect)
+    assert npw.bottomleft == (300, 975)
+
+    myPyBox.bottomright = (1000, 900)
+    time.sleep(timelap)
+    print(npw.box, npw.rect)
+    assert npw.bottomright == (1000, 900)
+
+    myPyBox.midleft = (300, 400)
+    time.sleep(timelap)
+    print(npw.box, npw.rect)
+    assert npw.midleft == (300, 400)
+
+    myPyBox.midright = (1050, 600)
+    time.sleep(timelap)
+    print(npw.box, npw.rect)
+    assert npw.midright == (1050, 600)
+
+    myPyBox.midtop = (500, 350)
+    time.sleep(timelap)
+    print(npw.box, npw.rect)
+    assert npw.midtop == (500, 350)
+
+    myPyBox.midbottom = (500, 800)
+    time.sleep(timelap)
+    print(npw.box, npw.rect)
+    assert npw.midbottom == (500, 800)
+
+    myPyBox.center = (500, 350)
+    time.sleep(timelap)
+    print(npw.box, npw.rect)
+    assert npw.center == (500, 350)
+
+    myPyBox.centerx = 1000
+    time.sleep(timelap)
+    print(npw.box, npw.rect)
+    assert npw.centerx == 1000
+
+    myPyBox.centery = 600
+    time.sleep(timelap)
+    print(npw.box, npw.rect)
+    assert npw.centery == 600
+
+    myPyBox.width = 700
+    time.sleep(timelap)
+    print(npw.box, npw.rect)
+    assert npw.width == 700
+
+    myPyBox.height = 400
+    time.sleep(timelap)
+    print(npw.box, npw.rect)
+    assert npw.height == 400
+
+    myPyBox.size = (551, 401)
+    time.sleep(timelap)
+    print(npw.box, npw.rect)
+    assert npw.size == (551, 401)
+
+    # Test closing
+    npw.close()
+
+
+def main() -> None:
     test_basic()
 
 
diff --git a/uv.lock b/uv.lock
index c7f7e7f..a01244f 100644
--- a/uv.lock
+++ b/uv.lock
@@ -8292,6 +8292,7 @@ dev = [
     { name = "myst-parser", version = "4.0.1", source = { registry = "https://pypi.org/simple" }, marker = "python_full_version == '3.10.*'" },
     { name = "myst-parser", version = "5.1.0", source = { registry = "https://pypi.org/simple" }, marker = "python_full_version >= '3.11'" },
     { name = "pywinctl" },
+    { name = "ruff" },
     { name = "types-python-xlib", version = "0.33.0.20250809", source = { registry = "https://pypi.org/simple" }, marker = "python_full_version < '3.10'" },
     { name = "types-python-xlib", version = "0.33.0.20260518", source = { registry = "https://pypi.org/simple" }, marker = "python_full_version >= '3.10'" },
     { name = "types-pywin32", version = "311.0.0.20251008", source = { registry = "https://pypi.org/simple" }, marker = "python_full_version < '3.10'" },
@@ -8317,6 +8318,7 @@ dev = [
     { name = "mypy", specifier = ">=0.990,<2" },
     { name = "myst-parser" },
     { name = "pywinctl", specifier = ">=0.3" },
+    { name = "ruff", specifier = ">=0.15.16" },
     { name = "types-python-xlib", specifier = ">=0.32" },
     { name = "types-pywin32", specifier = ">=305.0.0.3" },
 ]
@@ -8461,6 +8463,31 @@ wheels = [
     { url = "https://files.pythonhosted.org/packages/04/54/6f679c435d28e0a568d8e8a7c0a93a09010818634c3c3907fc98d8983770/roman_numerals-4.1.0-py3-none-any.whl", hash = "sha256:647ba99caddc2cc1e55a51e4360689115551bf4476d90e8162cf8c345fe233c7", size = 7676, upload-time = "2025-12-17T18:25:33.098Z" },
 ]
 
+[[package]]
+name = "ruff"
+version = "0.15.17"
+source = { registry = "https://pypi.org/simple" }
+sdist = { url = "https://files.pythonhosted.org/packages/8c/a9/3abdf488f1bf3d24c699415e454ed554a6350d5d89ce183be1ee0a3361ac/ruff-0.15.17.tar.gz", hash = "sha256:2ec446937fd16c8c4de2674a209cc5af64d9c6f17d21fbf1151054fa0bcf5219", size = 4743346, upload-time = "2026-06-11T17:54:47.663Z" }
+wheels = [
+    { url = "https://files.pythonhosted.org/packages/db/4d/e11259f5da07cb6afb2d074c31bf09da9671993f7329d4f15d2fdc458301/ruff-0.15.17-py3-none-linux_armv6l.whl", hash = "sha256:d9feddb927fc68bd295f5eebc587a7e42cfaf9b65f60ca4a2386febff575da8f", size = 10856677, upload-time = "2026-06-11T17:54:49.533Z" },
+    { url = "https://files.pythonhosted.org/packages/29/3e/772d679e1a0dc058e58875bd2c0cb713a0530877b4a76fee3c7966df0d49/ruff-0.15.17-py3-none-macosx_10_12_x86_64.whl", hash = "sha256:25805a226d741c47d274a35ad5c10a7dde175fcddfa511d7cf3da0a21eb3eab7", size = 11223443, upload-time = "2026-06-11T17:55:00.573Z" },
+    { url = "https://files.pythonhosted.org/packages/68/58/bd41f7688b2fd5623012605130ed70e60aa7f2244baa3d5066bdd61530c8/ruff-0.15.17-py3-none-macosx_11_0_arm64.whl", hash = "sha256:f6ad73b14c2d18a3bf8ad7cb6974294d7f613a7898604826058e6ac64918ef4d", size = 10566458, upload-time = "2026-06-11T17:55:07.52Z" },
+    { url = "https://files.pythonhosted.org/packages/d8/5b/733371013fcf1ec339e477ece6ab42bfe10bdd9bba8ee88a9516aa56bfc0/ruff-0.15.17-py3-none-manylinux_2_17_aarch64.manylinux2014_aarch64.whl", hash = "sha256:6ba0c1e4f95bcb3869d0d30cbd5917071ef2e28665abfec970cdab0492c713ed", size = 10914483, upload-time = "2026-06-11T17:55:05.501Z" },
+    { url = "https://files.pythonhosted.org/packages/bd/cc/6f24251cc0252f7239391ccb85833f320efad14ebe5b443943f37ced6332/ruff-0.15.17-py3-none-manylinux_2_17_armv7l.manylinux2014_armv7l.whl", hash = "sha256:81647960f10bff57d2e51cadd0c3950fe598400c852863a038720ef5b8cca91e", size = 10647497, upload-time = "2026-06-11T17:54:57.733Z" },
+    { url = "https://files.pythonhosted.org/packages/68/dd/0d10c17ce1a1624d6fc3156309c3f834fdb5dfaad026ec90c85684f3990e/ruff-0.15.17-py3-none-manylinux_2_17_i686.manylinux2014_i686.whl", hash = "sha256:0e01a84ddbc8c16c23055ba3924476850f1bbc1917cebbb9376665a63e74260d", size = 11416967, upload-time = "2026-06-11T17:54:51.461Z" },
+    { url = "https://files.pythonhosted.org/packages/2f/91/556bfb156f6144f355e831c23db00b2fc4120f86b3ce81cc5f7fd2df51f3/ruff-0.15.17-py3-none-manylinux_2_17_ppc64le.manylinux2014_ppc64le.whl", hash = "sha256:84fe9f653152f8f294f9f7e03bf3a453d8b4a27f7a59c78c8666167f2b17b96c", size = 12335770, upload-time = "2026-06-11T17:54:45.793Z" },
+    { url = "https://files.pythonhosted.org/packages/88/82/8b5999aa13355e926f06d9f42a32dcca862f623bf0363785ff89d607dffd/ruff-0.15.17-py3-none-manylinux_2_17_s390x.manylinux2014_s390x.whl", hash = "sha256:8c0fe88a7676e7a05b73174d4d4a59cb2ac21ff8263583f87a81a6018475a978", size = 11575441, upload-time = "2026-06-11T17:54:32.661Z" },
+    { url = "https://files.pythonhosted.org/packages/11/93/f10377bb04109ca0e8cbc483ff1982c54b6d418210041776f93e8cdc7fa9/ruff-0.15.17-py3-none-manylinux_2_17_x86_64.manylinux2014_x86_64.whl", hash = "sha256:ecfc3c7878fff94633ab0348524e093f9ce3243080416dd7d14f8ba400174719", size = 11557614, upload-time = "2026-06-11T17:54:34.698Z" },
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+    { url = "https://files.pythonhosted.org/packages/2d/c7/c53e8dbff9c9dc4b7928773421ae294a5d28fcb8dcda1a089579d3a7e510/ruff-0.15.17-py3-none-win_arm64.whl", hash = "sha256:f3be1fbb34bcdfd146240d8fb92a709d4c2c8191348580a3c044ec60fa0b4456", size = 11355275, upload-time = "2026-06-11T17:54:43.635Z" },
+]
+
 [[package]]
 name = "six"
 version = "1.17.0"