Don't try to test deprecation warnings on twisted < 8.2.0.

twisted.trial.unittest.TestCase.flushWarnings was added in 8.2.0.

master/buildbot/test/unit/test_process_factory.py

@@ -14,6 +14,8 @@
 # Copyright Buildbot Team Members
 
 from twisted.trial import unittest
+from twisted.python import versions
+import twisted
 from mock import Mock
 
 from buildbot.process.factory import BuildFactory, ArgumentsInTheWrongPlace, s
@@ -29,7 +31,8 @@ def test_init(self):
     def test_init_deprecated(self):
         factory = BuildFactory([s(BuildStep)])
         self.assertEqual(factory.steps, [(BuildStep, {})])
-        self.assertEqual(len(self.flushWarnings([BuildFactory.__init__])), 1)
+        if twisted.version >= versions.Version('twisted', 8, 2, 0):
+            self.assertEqual(len(self.flushWarnings([BuildFactory.__init__])), 1)
 
     def test_addStep(self):
         step = BuildStep()
@@ -41,7 +44,8 @@ def test_addStep_deprecated(self):
         factory = BuildFactory()
         factory.addStep(BuildStep)
         self.assertEqual(factory.steps, [(BuildStep, {})])
-        self.assertEqual(len(self.flushWarnings([BuildFactory.addStep])), 1)
+        if twisted.version >= versions.Version('twisted', 8, 2, 0):
+            self.assertEqual(len(self.flushWarnings([BuildFactory.addStep])), 1)
 
     def test_addStep_notAStep(self):
         factory = BuildFactory()