在 Python 模拟库中模拟 return 嵌套调用的值

Question

这个图书馆是全新的

这是我模拟对象的调用堆栈

[call(),
 call('test'),
 call().instance('test'),
 call().instance().database('test'),
 call().instance().database().snapshot(),
 call().instance().database().snapshot().__enter__(),
 call().instance().database().snapshot().__enter__().execute_sql('SELECT * FROM users'),
 call().instance().database().snapshot().__exit__(None, None, None),
 call().instance().database().snapshot().__enter__().execute_sql().__iter__()]

这是我用过的代码

    @mock.patch('testmodule.Client')
    def test_read_with_query(self, mock_client):
        mock = mock_client()
        pipeline = TestPipeline()
        records = pipeline | ReadFromSpanner(TEST_PROJECT_ID, TEST_INSTANCE_ID, self.database_id).with_query('SELECT * FROM users')
        pipeline.run()
        print mock_client.mock_calls
        exit()

我想模拟整个堆栈，最终它会给我一些假数据，我将这些数据作为 return 值提供。

正在测试的代码是


        spanner_client = Client(self.project_id)
        instance = spanner_client.instance(self.instance_id)
        database = instance.database(self.database_id)

        with database.snapshot() as snapshot:
            results = snapshot.execute_sql(self.query)

所以我的要求是 results 变量应该包含我将提供的数据。

如何为这样的嵌套调用提供 return 值

谢谢

Answer 1

要么直接给你的Mock实例设置值（那些enters和exit应该没见过）with:

mock.return_value.instance.return_value.database.return_value.snapshot.return_value.execute_sql.return_value = MY_MOCKED_DATA

或修补并设置 return_value 到目标方法，例如：

@mock.patch('database_engine.execute_sql', return_value=MY_MOCKED_DATA)

Answer 2

为被测代码中的 instance、database 和 snapshot 对象创建单独的 MagicMock 实例。使用 return_value 配置每个方法的 return 值。这是一个例子。我将被测方法简化为一个名为 mut 的独立函数。

# test_module.py : the module under test
class Client:
    pass

def mut(project_id, instance_id, database_id, query):
    spanner_client = Client(project_id)
    instance = spanner_client.instance(instance_id)
    database = instance.database(database_id)

    with database.snapshot() as snapshot:
        results = snapshot.execute_sql(query)
        return results

# test code (pytest)
from unittest.mock import MagicMock
from unittest import mock

from test_module import mut

@mock.patch('test_module.Client')
def test_read_with_query(mock_client_class):
    mock_client = MagicMock()
    mock_instance = MagicMock()
    mock_database = MagicMock()
    mock_snapshot = MagicMock()
    expected = 'fake query results'

    mock_client_class.return_value = mock_client
    mock_client.instance.return_value = mock_instance
    mock_instance.database.return_value = mock_database
    mock_database.snapshot.return_value = mock_snapshot
    mock_snapshot.execute_sql.return_value = expected
    mock_snapshot.__enter__.return_value = mock_snapshot

    observed = mut(29, 42, 77, 'select *')

    mock_client_class.assert_called_once_with(29)
    mock_client.instance.assert_called_once_with(42)
    mock_instance.database.assert_called_once_with(77)
    mock_database.snapshot.assert_called_once_with()
    mock_snapshot.__enter__.assert_called_once_with()
    mock_snapshot.execute_sql.assert_called_once_with('select *')
    assert observed == expected

这个测试有点胖。考虑使用固定装置和设置模拟的 before 函数将其分解。

在 Python 模拟库中模拟 return 嵌套调用的值

Mocking return value of a nested call in Python mock library

python

unit-testing

python-mock