While this looks harmless, I seriously question whether it is an improvement.  

For example, how is this any better?

-        self.assertTrue(operator.setitem(a, 0, 2) is None)
+        self.assertIsNone(operator.setitem(a, 0, 2))

This error message for the first is already perfectly clear.
I don't see anything that warrants the code churn.

Also remember that changing tests is hazardous.
We don't have tests for the tests.  So, if a test
gets damaged, we won't know about it.   The particular
patch seems fine, but the whole exercise of going through
the test suite and altering the tests is a dubious.  The
odds of us getting ANY value out of this is vanishingly small.