获取传递给 mock_open 的参数并为模拟调用不同的函数

Question

I'd like to use mock_open to mock the functionality of opening a file, however, I'd like to know the actual argument passed:

# module.py

file_path = "path/to/file"
with open(file_path, "r") as f:
    contents = f.read()

# test_module.py

from moto import mock_open
from unittest.mock import patch

def test_open():
    with patch("module.open", mock_open(
        with open(file_path) as f:
            contents = f.read()
        return contents
    ):

Now I know what you must be thinking, this is completely useless and stupid as it ruins the purpose of mock_open .

However, I actually want to mock a different function, namely, smart_open and instead of opening the file on S3, I have it in my local testing environment. Hence, I'd like to use the file_path passed to smart_open , and then use open to get the actual contents. I also cannot use open directly, since the file_path passed to smart_open has a prefix of s3:// and I'd like to get rid of it.

In essence, this is how it actually looks:

# module.py

from smart_open import open as smart_open

file_path = "s3://path/to/file"
with smart_open(file_path, "r") as f:
    contents = f.read()

# test_module.py

from moto import mock_open
from unittest.mock import patch
from utils import preprocess_path

def test_open():
    with patch("module.smart_open", mock_open(
        # something to pass to mock_open that says to do the following

        # get rid of the s3:// in the beginning
        file_path = preprocess_path(file_path)

        # get the contents using open instead of smart_open
        with open(file_path) as f:
            contents = f.read()

        return contents
    ):

Is it possible to do some preprocessing and call a different function (in this case open ) using the argument passed to smart_open ?

Answer 1

Do something like:

@mock.patch("blah.blah.boto3.Session")
def test_open(m_session):
    m_open = mock.mock_open()
    with patch("module.smart_open", m_open, create=True):
        do_writing_function()
        m_open.return_value.write.assert_called_once_with(expected_stuff)

Basically you patch out smart_open's open with the mock_open, then you can read what mock_open's write is called with. call_args_list should also work here.

I patched boto3.Session myself to avoid dealing with the session stuff in my module, but since open is mocked, you won't actually try to open anything from the given filepath in the test.

In my case, I also had my open()/writing in a separate function, which you might want to do as well.