Add test for Linearizer.is_queued(..)

tests/util/test_linearizer.py

@@ -45,6 +45,38 @@ class LinearizerTestCase(unittest.TestCase):
         with (yield d2):
             pass
 
+    @defer.inlineCallbacks
+    def test_linearizer_is_queued(self):
+        linearizer = Linearizer()
+
+        key = object()
+
+        d1 = linearizer.queue(key)
+        cm1 = yield d1
+
+        # Since d1 gets called immediately, "is_queued" should return false.
+        self.assertFalse(linearizer.is_queued(key))
+
+        d2 = linearizer.queue(key)
+        self.assertFalse(d2.called)
+
+        # Now d2 is queued up behind successful completion of cm1
+        self.assertTrue(linearizer.is_queued(key))
+
+        with cm1:
+            self.assertFalse(d2.called)
+
+            # cm1 still not done, so d2 still queued.
+            self.assertTrue(linearizer.is_queued(key))
+
+        # And now d2 is called and nothing is in the queue again
+        self.assertFalse(linearizer.is_queued(key))
+
+        with (yield d2):
+            self.assertFalse(linearizer.is_queued(key))
+
+        self.assertFalse(linearizer.is_queued(key))
+
     def test_lots_of_queued_things(self):
         # we have one slow thing, and lots of fast things queued up behind it.
         # it should *not* explode the stack.