使用单元测试和模拟修补 python 函数中的变量

Question

I have the following my_func.py with create_config function.

*my_func.py

from fabric.state import env

def create_config(node_name):
    config = {
    "log_level": "INFO",
    "addr1": "127.0.0.1",
    }
    config["addr2"] = env.host
    return config

I tried the following approach to mock env.host variable where env is an import from fabric.state.

*test.py

import unittest
import my_func
import mock


class MyTestCase(unittest.TestCase):
    def setUp(self):
        self.master_config = {
              "log_level": "INFO",
              "addr2": "0.0.0.0",
              "addr1": "127.0.0.1",
        }

    @mock.patch('env.host')
    def test_create_consul_config(self, mock_host):
        mock_host.return_value = "0.0.0.0"
        result = my_func.create_config('master')
        self.assertDictEqual(self.master_config, result)


if __name__ == '__main__':
    unittest.main()

I am getting import error with 'env'. What is the best way to mock variable within a function with python mock.

ImportError: No module named env

Answer 1

mock variable env.host ?

get the type of env first

In [6]: from fabric.state import env

In [7]: type(env)
Out[7]: fabric.utils._AttributeDict

env.host is instance variable of a class, the mock is a little different, mock_env is object(AttributeDict), the assignment of instance_variable host is direct assignment, not with a return_value

@mock.patch('my_func.env')
def test_create_consul_config(self, mock_env):
    mock_env.host = 'xxx'
    result = my_func.create_config('master')

    self.assertDictEqual(self.master_config, result)

Answer 2

From the unittest.mock documentation on patch (note target is the first argument of patch ):

target should be a string in the form 'package.module.ClassName'. The target is imported and the specified object replaced with the new object, so the target must be importable from the environment you are calling patch() from. The target is imported when the decorated function is executed, not at decoration time.

So you need to include the full path to the function you are patching. Note also in where to patch that the target should be the path to where the function/object is used, not where it is defined.

So changing your patch call to:

@mock.patch("my_func.env.host")

should fix the ImportError .