My Class just like 

```
import a

class Demo(object):
    def __init__(self):
        ......
        fun_return_value = a.methodB()
        ......

   def methodA(self):
       ......

```

the test class just like below

```
class TestDemo(test.TestCase):

    def setUp(self):
        super(TestDemo, self).setUp()

    def test_methodA(self):
         ......

```

When I want to make methodA's unittest, there has the question that I must mock the a.methodB.But how can I do that?I checked the doc,and found nothing.
Ask others and use `@mock.patch("a.methodB")` at the head of the class TestDemo.Just like

```
    @mock.patch("a.methodB")
    class TestDemo(test.TestCase):

        def setUp(self, mock_methodB):
            super(TestDemo, self).setUp()
            mock_methodB.return_value=None

        def test_methodA(self):
             ......

```

But it didn't work.How to mock the method which was called by the method of "**init**"?