Test SignalManager.disconnect_all() (#7625)

tests/test_signalmanager.py

@@ -0,0 +1,21 @@
+from scrapy.signalmanager import SignalManager
+
+
+class TestSignalManager:
+    def test_disconnect_all(self):
+        signal = object()
+        sender = object()
+        sm = SignalManager(sender)
+
+        calls = []
+
+        def handler():
+            calls.append(1)
+
+        sm.connect(handler, signal)
+        sm.send_catch_log(signal)
+        assert calls == [1]
+
+        sm.disconnect_all(signal)
+        sm.send_catch_log(signal)
+        assert calls == [1]  # handler no longer called after disconnect_all