Rewrite cache list decorator

Because it was complicated and annoyed me. I suspect this will be more
efficient too.

tests/util/caches/test_descriptors.py

@@ -273,3 +273,64 @@ class DescriptorTestCase(unittest.TestCase):
         r = yield obj.fn(2, 3)
         self.assertEqual(r, 'chips')
         obj.mock.assert_not_called()
+
+
+@unittest.DEBUG
+class CachedListDescriptorTestCase(unittest.TestCase):
+    @defer.inlineCallbacks
+    def test_cache(self):
+        class Cls(object):
+            def __init__(self):
+                self.mock = mock.Mock()
+
+            @descriptors.cached()
+            def fn(self, arg1, arg2):
+                pass
+
+            @descriptors.cachedList("fn", "args1", inlineCallbacks=True)
+            def list_fn(self, args1, arg2):
+                assert (
+                    logcontext.LoggingContext.current_context().request == "c1"
+                )
+                # we want this to behave like an asynchronous function
+                yield run_on_reactor()
+                assert (
+                    logcontext.LoggingContext.current_context().request == "c1"
+                )
+                defer.returnValue(self.mock(args1, arg2))
+
+        with logcontext.LoggingContext() as c1:
+            c1.request = "c1"
+            obj = Cls()
+            obj.mock.return_value = {10: 'fish', 20: 'chips'}
+            d1 = obj.list_fn([10, 20], 2)
+            self.assertEqual(
+                logcontext.LoggingContext.current_context(),
+                logcontext.LoggingContext.sentinel,
+            )
+            r = yield d1
+            self.assertEqual(
+                logcontext.LoggingContext.current_context(),
+                c1
+            )
+            obj.mock.assert_called_once_with([10, 20], 2)
+            self.assertEqual(r, {10: 'fish', 20: 'chips'})
+            obj.mock.reset_mock()
+
+            # a call with different params should call the mock again
+            obj.mock.return_value = {30: 'peas'}
+            r = yield obj.list_fn([20, 30], 2)
+            obj.mock.assert_called_once_with([30], 2)
+            self.assertEqual(r, {20: 'chips', 30: 'peas'})
+            obj.mock.reset_mock()
+
+            # all the values should now be cached
+            r = yield obj.fn(10, 2)
+            self.assertEqual(r, 'fish')
+            r = yield obj.fn(20, 2)
+            self.assertEqual(r, 'chips')
+            r = yield obj.fn(30, 2)
+            self.assertEqual(r, 'peas')
+            r = yield obj.list_fn([10, 20, 30], 2)
+            obj.mock.assert_not_called()
+            self.assertEqual(r, {10: 'fish', 20: 'chips', 30: 'peas'})