This test passed in Python <= 3.3 but fails in 3.4:

    def testTestSuiteConsumesTest(self):
        class MyTestCase(unittest.TestCase):
            def testMethod(self):
                pass
        test = MyTestCase('testMethod')
        suite = unittest.TestSuite((test,))
        result = unittest.TestResult()
        self.assertEqual(next(iter(suite)), test)
        suite.run(result)
        self.assertEqual(next(iter(suite)), test)

The suite contains None after it has been run in Python 3.4.

This is presumably a consequence of issue 11798.  How did you run into it in actual code?

I have some complex test fixtures that I have written tests for, and one of them started to fail because it assumed that the suite would still be valid after having run.

That said, I was able to work around the issue and if you don't care neither do I. ;-)

The new behaviour is intentional, glad you've managed to work around it.