test(threading): Add test for ThreadPoolExecutor (#2259)

ThreadPoolExecutor also obeys hub propagation, but there wasn't a test for it. This PR adds a bit more coverage.

---------

Co-authored-by: Neel Shah <neelshah.sa@gmail.com>
Co-authored-by: Anton Pirker <anton.pirker@sentry.io>

tests/integrations/threading/test_threading.py

@@ -2,8 +2,14 @@
 import sys
 from threading import Thread
 
+try:
+    from concurrent import futures
+except ImportError:
+    futures = None
+
 import pytest
 
+import sentry_sdk
 from sentry_sdk import configure_scope, capture_message
 from sentry_sdk.integrations.threading import ThreadingIntegration
 
@@ -73,6 +79,42 @@ def stage2():
         assert "stage1" not in event.get("tags", {})
 
 
+@pytest.mark.skipif(
+    futures is None,
+    reason="ThreadPool was added in 3.2",
+)
+@pytest.mark.parametrize("propagate_hub", (True, False))
+def test_propagates_threadpool_hub(sentry_init, capture_events, propagate_hub):
+    sentry_init(
+        traces_sample_rate=1.0,
+        integrations=[ThreadingIntegration(propagate_hub=propagate_hub)],
+    )
+    events = capture_events()
+
+    def double(number):
+        with sentry_sdk.start_span(op="task", description=str(number)):
+            return number * 2
+
+    with sentry_sdk.start_transaction(name="test_handles_threadpool"):
+        with futures.ThreadPoolExecutor(max_workers=1) as executor:
+            tasks = [executor.submit(double, number) for number in [1, 2, 3, 4]]
+            for future in futures.as_completed(tasks):
+                print("Getting future value!", future.result())
+
+    sentry_sdk.flush()
+
+    if propagate_hub:
+        assert len(events) == 1
+        (event,) = events
+        assert event["spans"][0]["trace_id"] == event["spans"][1]["trace_id"]
+        assert event["spans"][1]["trace_id"] == event["spans"][2]["trace_id"]
+        assert event["spans"][2]["trace_id"] == event["spans"][3]["trace_id"]
+        assert event["spans"][3]["trace_id"] == event["spans"][0]["trace_id"]
+    else:
+        (event,) = events
+        assert len(event["spans"]) == 0
+
+
 def test_circular_references(sentry_init, request):
     sentry_init(default_integrations=False, integrations=[ThreadingIntegration()])