Backed out changeset 54e4545b0fe0 (bug 1380338) for breaking spidermonkey pkg due to failing to process taskgraph/test/python.ini. r=backout

taskcluster/mach_commands.py

@@ -70,6 +70,17 @@ class MachCommands(MachCommandBase):
         and that build may further depend on various toolchains, libraries, etc.
         """
 
+    @SubCommand('taskgraph', 'python-tests',
+                description='Run the taskgraph unit tests')
+    def taskgraph_python_tests(self, **options):
+        import unittest
+        import mozunit
+        suite = unittest.defaultTestLoader.discover('taskgraph.test')
+        runner = mozunit.MozTestRunner(verbosity=2)
+        result = runner.run(suite)
+        if not result.wasSuccessful():
+            sys.exit(1)
+
     @ShowTaskGraphSubCommand('taskgraph', 'tasks',
                              description="Show all tasks in the taskgraph")
     def taskgraph_tasks(self, **options):