在mock中嵌套spec_set

Question

我有两个以下文件：

testcase_module.py

import boto3


ec2 = boto3.resource('ec2')


def f():
    return ec2.instances.all()

testcase_test.py

import testcase_module
import unittest.mock


class MainTest(unittest.TestCase):
    @unittest.mock.patch('testcase_module.ec2', spec_set=['instances'])
    def test_f(self, ec2_mock):
        ec2_mock.instances.spec_set = ['all']
        testcase_module.f()


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

我在补丁中添加了spec_test参数，因为我想断言是否调用了除instances.all()以外的任何其他函数，但是将字符串'all'更改为'allx'并不是将'instances'更改为'instancesx'时，测试失败。我尝试了以下更改（以下git diff testcase_test.py和python testcase_test.py结果）：

尝试1：

diff --git a/testcase_test.py b/testcase_test.py
index d6d6e59..ae274c8 100644
--- a/testcase_test.py
+++ b/testcase_test.py
@@ -3,9 +3,8 @@ import unittest.mock


 class MainTest(unittest.TestCase):
-    @unittest.mock.patch('testcase_module.ec2', spec_set=['instances'])
-    def test_f(self, ec2_mock):
-        ec2_mock.instances.spec_set = ['all']
+    @unittest.mock.patch('testcase_module.ec2', spec_set=['instances.all'])
+    def test_f(self, _):
         testcase_module.f()

产地：

E
======================================================================
ERROR: test_f (__main__.MainTest)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/usr/lib/python3.5/unittest/mock.py", line 1157, in patched
    return func(*args, **keywargs)
  File "testcase_test.py", line 8, in test_f
    testcase_module.f()
  File "/path/to/project/testcase_module.py", line 8, in f
    return ec2.instances.all()
  File "/usr/lib/python3.5/unittest/mock.py", line 578, in __getattr__
    raise AttributeError("Mock object has no attribute %r" % name)
AttributeError: Mock object has no attribute 'instances'

----------------------------------------------------------------------
Ran 1 test in 0.001s

FAILED (errors=1)

尝试2：

diff --git a/testcase_test.py b/testcase_test.py
index d6d6e59..d93abd1 100644
--- a/testcase_test.py
+++ b/testcase_test.py
@@ -3,9 +3,8 @@ import unittest.mock


 class MainTest(unittest.TestCase):
-    @unittest.mock.patch('testcase_module.ec2', spec_set=['instances'])
-    def test_f(self, ec2_mock):
-        ec2_mock.instances.spec_set = ['all']
+    @unittest.mock.patch('testcase_module.ec2.instances', spec_set=['all'])
+    def test_f(self):
         testcase_module.f()

产地：

E
======================================================================
ERROR: test_f (__main__.MainTest)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/usr/lib/python3.5/unittest/mock.py", line 1149, in patched
    arg = patching.__enter__()
  File "/usr/lib/python3.5/unittest/mock.py", line 1312, in __enter__
    setattr(self.target, self.attribute, new_attr)
AttributeError: can't set attribute

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/usr/lib/python3.5/unittest/mock.py", line 1170, in patched
    patching.__exit__(*exc_info)
  File "/usr/lib/python3.5/unittest/mock.py", line 1334, in __exit__
    delattr(self.target, self.attribute)
AttributeError: can't delete attribute

----------------------------------------------------------------------
Ran 1 test in 0.001s

FAILED (errors=1)

如果调用了instances.all之外的其他方法，怎么能让它失败？

Answer 1

尝试使用mock_add_spec。

ec2_mock.instances.mock_add_spec(['all'], spec_set=True)

链接：https://docs.python.org/3/library/unittest.mock.html#unittest.mock.Mock.mock_add_spec

Answer 2

这样做是怎么回事：

@unittest.mock.patch('testcase_module.boto3.resource', autospec=True)
def test_f(self, ec2_resource_mock):
    class InstanceStub(object):
        def all(self):
            return [...]
    ec2_resource_mock.return_value = mock.create_autospec(
        EC2InstanceType, instances=InstanceStub())
    testcase_module.f()