Python does not allow assignment to anything but the innermost local scope or
the global scope with the
global keyword. This presents a problem when
creating nested functions:
def test_localVariable(self): cb_called = False def cb(): cb_called = True cb() self.assertTrue(cb_called) # will fail!
cb_called = True assigns to a different variable than
cb_called = False. In production code, it's usually best to work around
such problems, but in tests this is often the clearest way to express the
behavior under test.
The solution is to change something in a common mutable object. While a simple
list can serve as such a mutable object, this leads to code that is hard to
read. Instead, use
from buildbot.test.state import State def test_localVariable(self): state = State(cb_called=False) def cb(): state.cb_called = True cb() self.assertTrue(state.cb_called) # passes
This is almost as readable as the first example, but it actually works.