diff --git a/etc/ci/taskcluster/decisionlib.py b/etc/ci/taskcluster/decisionlib.py
index 70bfb82cdea..c941f4915ab 100644
--- a/etc/ci/taskcluster/decisionlib.py
+++ b/etc/ci/taskcluster/decisionlib.py
@@ -194,7 +194,7 @@ class DecisionTask:
 
         task_id = taskcluster.slugId().decode("utf8")
         self.queue_service.createTask(task_id, payload)
-        print("Scheduled %s: %s" % (task_name, task_id))
+        print("Scheduled %s" % task_name)
         return task_id
 
 
diff --git a/etc/ci/taskcluster/mock.py b/etc/ci/taskcluster/mock.py
new file mode 100755
index 00000000000..dc0ba65b192
--- /dev/null
+++ b/etc/ci/taskcluster/mock.py
@@ -0,0 +1,36 @@
+#!/usr/bin/python3
+
+# Copyright 2018 The Servo Project Developers. See the COPYRIGHT
+# file at the top-level directory of this distribution.
+#
+# Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+# http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+# <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+# option. This file may not be copied, modified, or distributed
+# except according to those terms.
+
+"""
+Run the decision task with fake Taskcluster APIs, to catch Python errors before pushing.
+"""
+
+import os
+import sys
+from unittest.mock import MagicMock
+
+
+class TaskclusterRestFailure(Exception):
+    status_code = 404
+
+
+class Index:
+    def __init__(self, options):
+        pass
+
+    def findTask(self, _):
+        raise TaskclusterRestFailure
+
+
+Queue = stringDate = fromNow = slugId = os.environ = MagicMock()
+sys.modules["taskcluster"] = sys.modules[__name__]
+sys.dont_write_bytecode = True
+exec(open("decision-task.py").read())