Python单元测试：正确Mock类方法中条件分支的内部函数调用

from dataclasses import dataclass, ClassVar
from unittest.mock import patch, MagicMock

# 假设这些是外部模块中的函数
def feature_flag():
    # 模拟一个外部特性开关
    return False

def get_sync_column():
    # 模拟一个返回同步列名的函数
    return "default_sync_column"

@dataclass(frozen=True)
class RMTable():
    sync_column: ClassVar[str] = None

    def __post_init__(self) -> None:
        if self.sync_column is None:
            object.__setattr__(self, "sync_column", self.cal_sync_column())

    def cal_sync_column(self) -> str:
        if not feature_flag():
            return "_synced"
        else:
            return get_sync_column() # 这个函数是我们想要测试其被调用的情况

from unittest.mock import patch, MagicMock
from my_module import RMTable, feature_flag, get_sync_column # 假设这些在my_module中

def test_sync_column_initial_attempt():
    with patch("my_module.feature_flag") as feature_flag_mock:
        with patch("my_module.get_sync_column") as mock_sync_column:
            feature_flag_mock.return_value = True # 强制进入else分支

            # 错误的方法：模拟整个RMTable实例
            rm_table_mock = MagicMock(spec=RMTable)
            rm_table_mock.cal_sync_column.return_value = "FLAG_1" # 为mock的方法设置返回值

            result = rm_table_mock.cal_sync_column() # 调用mock的cal_sync_column

            assert result == "FLAG_1"
            mock_sync_column.assert_called_once() # 断言get_sync_column被调用

AssertionError: Expected 'get_sync_column' to have been called once. Called 0 times.

from unittest.mock import patch, MagicMock
from my_module import RMTable, feature_flag, get_sync_column # 确保导入了真实的RMTable

def test_sync_column_correct_approach():
    with patch("my_module.feature_flag") as feature_flag_mock:
        with patch("my_module.get_sync_column") as mock_sync_column:
            feature_flag_mock.return_value = True # 强制进入else分支

            # 关键改变：创建RMTable的真实实例
            rm_table = RMTable() 

            # 为被cal_sync_column内部调用的mock函数设置返回值
            mock_sync_column.return_value = "FLAG_1" 

            # 调用RMTable真实实例上的cal_sync_column方法
            result = rm_table.cal_sync_column() 

            assert result == "FLAG_1"
            mock_sync_column.assert_called_once() # 断言get_sync_column被调用
            print("Test passed: get_sync_column was called once and returned 'FLAG_1'")

# 示例运行（如果 my_module 存在并包含上述定义）
if __name__ == '__main__':
    # 为了让这个示例在没有真实my_module文件的情况下运行，我们重新定义RMTable和相关函数
    # 在实际项目中，你只需从my_module导入即可
    def feature_flag():
        return False
    def get_sync_column():
        return "default_sync_column"

    @dataclass(frozen=True)
    class RMTable():
        sync_column: ClassVar[str] = None

        def __post_init__(self) -> None:
            if self.sync_column is None:
                object.__setattr__(self, "sync_column", self.cal_sync_column())

        def cal_sync_column(self) -> str:
            if not feature_flag():
                return "_synced"
            else:
                return get_sync_column()

    # 将函数和类放入一个临时的“模块”命名空间中，以便patch能找到它们
    import sys
    sys.modules['my_module'] = sys.modules[__name__] # 模拟当前文件是my_module

    test_sync_column_correct_approach()