def test_popSingle(self):
        ctx = _ExecutionContext()
        a = object()
        ctx.push(a)
        ctx.pop()
        self.assertIs(ctx.current(), None)
L{_ExecutionContext.pop} cancels a L{_ExecutionContext.push}, leading
dataset/ETHPy150Open ClusterHQ/eliot/eliot/tests/test_action.py/ExecutionContextTests.test_popSingle