Test start and stop methods

Got in a bit of a pickle to make the thread initialization testable.
When `client.start()` was called, a thread was spawned, so I had to
implement a way to stop these threads from executing during other
tests (hence `client.stop()`)

All other tests continue to call `_run_probes` directly because the
resulting behaviour is easier to reason about.

conftest.py

@@ -15,6 +15,7 @@
 from opentelemetry.sdk.trace.export.in_memory_span_exporter import InMemorySpanExporter
 from opentelemetry.trace import set_tracer_provider
 
+from appsignal import probes
 from appsignal.agent import agent
 from appsignal.opentelemetry import METRICS_PREFERRED_TEMPORALITY
 
@@ -87,13 +88,11 @@ def remove_logging_handlers_after_tests():
 
 
 @pytest.fixture(scope="function", autouse=True)
-def remove_probes_after_tests():
+def stop_and_clear_probes_after_tests():
     yield
 
-    from appsignal.probes import _probes, _probe_states
-
-    _probes.clear()
-    _probe_states.clear()
+    probes.stop()
+    probes.clear()
 
 
 @pytest.fixture(scope="function", autouse=True)

src/appsignal/probes.py

@@ -2,9 +2,9 @@
 
 import logging
 from inspect import signature
-from threading import Lock, Thread
-from time import gmtime, sleep
-from typing import Any, Callable, NoReturn, Optional, TypeVar, Union, cast
+from threading import Event, Lock, Thread
+from time import gmtime
+from typing import Any, Callable, Optional, TypeVar, Union, cast
 
 
 T = TypeVar("T")
@@ -15,6 +15,7 @@
 _probe_states: dict[str, Any] = {}
 _lock: Lock = Lock()
 _thread: Thread | None = None
+_stop_event: Event = Event()
 
 
 def start() -> None:
@@ -24,12 +25,15 @@ def start() -> None:
         _thread.start()
 
 
-def _minutely_loop() -> NoReturn:
-    sleep(_initial_wait_time())
+def _minutely_loop() -> None:
+    wait_time = _initial_wait_time()
 
     while True:
+        if _stop_event.wait(timeout=wait_time):
+            break
+
         _run_probes()
-        sleep(_wait_time())
+        wait_time = _wait_time()
 
 
 def _run_probes() -> None:
@@ -88,3 +92,18 @@ def unregister(name: str) -> None:
             del _probes[name]
         if name in _probe_states:
             del _probe_states[name]
+
+
+def stop() -> None:
+    global _thread
+    if _thread is not None:
+        _stop_event.set()
+        _thread.join()
+        _thread = None
+        _stop_event.clear()
+
+
+def clear() -> None:
+    with _lock:
+        _probes.clear()
+        _probe_states.clear()

tests/test_probes.py

@@ -1,6 +1,15 @@
+from time import sleep
 from typing import Any, Callable, cast
 
-from appsignal.probes import _probe_states, _probes, _run_probes, register, unregister
+from appsignal.probes import (
+    _probe_states,
+    _probes,
+    _run_probes,
+    register,
+    start,
+    stop,
+    unregister,
+)
 
 
 def test_register(mocker):
@@ -32,7 +41,7 @@ def test_register_with_state(mocker):
     probe.assert_called_with("state")
 
 
-def test_register_signatures(mocker):
+def test_register_signatures():
     # `mocker.Mock` is not used here because we want to test against
     # specific function signatures.
 
@@ -107,3 +116,23 @@ def test_unregister(mocker):
     assert "probe_name" not in _probes
     assert "probe_name" not in _probe_states
     probe.assert_called_once_with(None)
+
+
+def test_start_stop(mocker):
+    mocker.patch("appsignal.probes._initial_wait_time").return_value = 0.001
+    mocker.patch("appsignal.probes._wait_time").return_value = 0.001
+
+    probe = mocker.Mock()
+    register("probe_name", probe)
+    start()
+
+    sleep(0.05)
+
+    probe.assert_called()
+
+    stop()
+    call_count = probe.call_count
+
+    sleep(0.05)
+
+    assert probe.call_count == call_count