无法使用pytest-mock模拟方法

Question

我有一个“MyClass”类，代码如下所示。

class MyClass:

    def __init__(update_type_id='1')
        
        self.update_type_id = update_type_id
        self._cursor = <database_connection).cursor()

    def update_start_dt(self):
        self._update_job_ctrl_start_dt()
        
    def _update_job_ctrl_start_dt(self):
        update_sql, v_1  = self._get_update_sql(self._update_type_id)
        logger.debug(f'Update sql: {update_sql} and v_1: {v_1}')
                
    def _get_update_sql(self, update_type_id: int) -> Tuple:
        sql = f"SELECT start_sql, end_sql FROM <database.table> where update_type_key = {self._update_type_id}"
        self._run_sql(sql)
        record = self._cursor.fetchone()
        if record:
            return record
        else:
            logger.error(f'Record Not Found. Update type key ({update_type_id}) not found in the table in the database')
            raise Exception


    def _run_sql(self, sql_statement: str):
        try:
            self._cursor.execute(sql_statement)
        except (Exception, Error) as e:
            logger.error(f'Error {e} encountered when reading from table')
            raise e

我正在尝试使用pytest-mock编写一个测试函数，这将测试update_start_dt方法。该方法在内部调用一系列私有方法，我很难模拟贯穿所有私有方法的代码。有人能帮我弄明白我们能用什么方式嘲笑吗？

我试图参考多个在线网站，但无法得到一个完整的图片。

class TestMyClass:
    
    def test_update_start_dt(mocker,mock_get_connection,mock_run_sql):
    
        mock_manager = mocker.Mock()
        mock_get_update_sql = mock_manager.patch('MyClass._get_update_sql')
        mock_get_update_sql.return_value = ('123','234')
        myclass = MyClass(update_type_id='1')
        
        myclass.update_start_dt()

以上测试代码的错误如下所示

update_sql, v_1  = self._get_update_sql(self._update_type_id)
ValueError: not enough values to unpack (expected 2, got 0)

Answer 1

这里的问题是，您正在对正在创建的Mock对象进行修补，为了测试的目的，您不需要显式地创建Mock对象。下面展示了如何测试它，我们直接在类上进行patch测试。

class MyClass:

    def __init__(self, update_type_id='1'):
        
        self._update_type_id = update_type_id
        self._cursor = None

    def update_start_dt(self):
        self._update_job_ctrl_start_dt()
        
    def _update_job_ctrl_start_dt(self):
        update_sql, v_1  = self._get_update_sql(self._update_type_id)
        logger.debug(f'Update sql: {update_sql} and v_1: {v_1}')
                
    def _get_update_sql(self, update_type_id: int):
        sql = f"SELECT start_sql, end_sql FROM <database.table> where update_type_key = {self._update_type_id}"
        self._run_sql(sql)
        record = self._cursor.fetchone()
        if record:
            return record
        else:
            logger.error(f'Record Not Found. Update type key ({update_type_id}) not found in the table in the database')
            raise Exception


    def _run_sql(self, sql_statement: str):
        try:
            self._cursor.execute(sql_statement)
        except (Exception, Error) as e:
            logger.error(f'Error {e} encountered when reading from table')
            raise e



def test_update_start_dt(mocker):
    mock_get_update_sql = mocker.patch.object(MyClass, "_get_update_sql")
    mock_get_update_sql.return_value = ("123", "234")
    myclass = MyClass(update_type_id='1')

    myclass.update_start_dt()

=========================================== test session starts ============================================
platform darwin -- Python 3.8.9, pytest-7.0.1, pluggy-1.0.0
rootdir: ***
plugins: mock-3.7.0
collected 1 item                                                                                           

test_script.py .                                                                                     [100%]

======================================= 1 passed, 1 warning in 0.01s =======================================

如果调用创建的Mock对象而不是类，代码就会工作。如下所示。

def test_update_start_dt(mocker):
    mock_manager = mocker.Mock()
    mock_get_update_sql = mock_manager.patch('MyClass._get_update_sql')
    mock_get_update_sql.return_value = ('123','234')
    # Notice how we use `mock_manager` instead of MyClass
    # tests will now pass
    myclass = mock_manager(update_type_id='1')
    
    myclass.update_start_dt()

希望你能看到现在的问题。