refactor test setups towards fixtures and hinting

src/watchdog/observers/__init__.py

@@ -54,13 +54,12 @@
 
 import sys
 import warnings
-from typing import Type
 
 from watchdog.utils import UnsupportedLibc
 
-from .api import BaseObserver
+from .api import BaseObserverSubclassCallable
 
-Observer: Type[BaseObserver]
+Observer: BaseObserverSubclassCallable
 
 
 if sys.platform.startswith("linux"):

src/watchdog/observers/api.py

@@ -19,7 +19,7 @@
 import threading
 from pathlib import Path
 
-from watchdog.utils import BaseThread
+from watchdog.utils import BaseThread, Protocol
 from watchdog.utils.bricks import SkipRepeatsQueue
 
 DEFAULT_EMITTER_TIMEOUT = 1  # in seconds.
@@ -379,3 +379,8 @@ def dispatch_events(self, event_queue):
                 if handler in self._handlers.get(watch, []):
                     handler.dispatch(event)
         event_queue.task_done()
+
+
+class BaseObserverSubclassCallable(Protocol):
+    def __call__(self, timeout: float = ...) -> BaseObserver:
+        ...

src/watchdog/utils/__init__.py

@@ -32,6 +32,7 @@
 
 import sys
 import threading
+from typing import TYPE_CHECKING
 
 
 class UnsupportedLibc(Exception):
@@ -136,3 +137,14 @@ def load_class(dotted_path):
         raise AttributeError(
             f"Module {module_name} does not have class attribute {klass_name}"
         )
+
+
+if TYPE_CHECKING or sys.version_info >= (3, 8):
+    # using `as` to explicitly re-export this since this is a compatibility layer
+    from typing import Protocol as Protocol
+else:
+    # Provide a dummy Protocol class when not available from stdlib.  Should be used
+    # only for hinting.  This could be had from typing_protocol, but not worth adding
+    # the _first_ dependency just for this.
+    class Protocol:
+        ...

tests/conftest.py

@@ -1,12 +1,15 @@
 from __future__ import annotations
 
+import contextlib
 import gc
 import os
 import threading
 from functools import partial
 
 import pytest
 
+from .utils import ExpectEvent, Helper, P, StartWatching, TestEventQueue
+
 
 @pytest.fixture()
 def p(tmpdir, *args):
@@ -51,3 +54,29 @@ def no_warnings(recwarn):
         warnings.append("{w.filename}:{w.lineno} {w.message}".format(w=warning))
     print(warnings)
     assert not warnings
+
+
+@pytest.fixture(name="helper")
+def helper_fixture(tmpdir):
+    with contextlib.closing(Helper(tmp=os.fspath(tmpdir))) as helper:
+        yield helper
+
+
+@pytest.fixture(name="p")
+def p_fixture(helper: Helper) -> P:
+    return helper.joinpath
+
+
+@pytest.fixture(name="event_queue")
+def event_queue_fixture(helper: Helper) -> TestEventQueue:
+    return helper.event_queue
+
+
+@pytest.fixture(name="start_watching")
+def start_watching_fixture(helper: Helper) -> StartWatching:
+    return helper.start_watching
+
+
+@pytest.fixture(name="expect_event")
+def expect_event_fixture(helper: Helper) -> ExpectEvent:
+    return helper.expect_event