how can I use fixture to create a mock file of certain size?

I’m doing something like this

def test_collection_size(create_fake_file):
    files = [create_fake_file]
    size = get_collection_size(files)
    assert size == 32

create_fake_file fixture should return a mock file of size 32 bytes

I did something like this

@pytest.fixture
def fake_file_content():
    # Returns 32 bytes of space
    return b" " * 32


@pytest.fixture
def create_fake_file(fake_file_content):
    def _create_fake_file(file_path):
        # Use unittest.mock.mock_open to create a mock file object
        mock_file = Mock(spec=open, read=Mock(return_value=fake_file_content))

        # Use unittest.mock.patch to replace the built-in open function with the mock_file
        with pytest.patch("builtins.open", mock_open(read_data=mock_file.read)):
            # Write the fake content to the specified file path
            with open(file_path, "wb") as file:
                file.write(fake_file_content)

    return _create_fake_file

• I’m getting TypeError: stat: path should be string, bytes, os.PathLike or integer, not function

>Solution :

First, I would recommend not mocking. Why do you need to mock out the file system?

Pytest has the feature to create mock directories & files for testing.

Do something like this

@pytest.fixture(scope="session")
def create_fake_file(tmp_path_factory):
    # Create a temporary file in the tmp_path directory
    temp_file = tmp_path_factory.mktemp("temp") / "temp_file.txt"

    # Write 32 bytes of data to the file
    temp_file.write_bytes(b"a" * 32)

    return temp_file

# test
def test_collection_size(create_fake_file):
    files = [create_fake_file]
    size = get_collection_size(files)
    assert size == 32