Mock out the contents of several files with a single patch

mock_open_with_files.py

from mock import MagicMock

def mock_open_with_files(files):
    """
    `files` - a dictionary of the form
    {
        '/file/path/': 'file body',
        ...
    }
    """
    file_mocks = {path: StringIO(body) for path, body in files.iteritems()}
    mock_open = MagicMock()
    mock_open.side_effect = lambda path, *args: MagicMock(
        wraps=file_mocks[path], __enter__=MagicMock(return_value=file_mocks[path]))
    mock_open.__enter__.side_effect = lambda path, *args: file_mocks[path]
    return mock_open