I'm using python-mock to mock out a file open call. I would like to be able to pass in fake data this way, so I can verify that read() is being called as well as using test data without hitting the filesystem on tests.
Here's what I've got so far:
file_mock = MagicMock(spec=file)
file_mock.read.return_value = 'test'
with patch('__builtin__.open', create=True) as mock_open:
mock_open.return_value = file_mock
with open('x') as f:
print f.read()
The output of this is <mock.Mock object at 0x8f4aaec> intead of 'test' as I would assume. What am I doing wrong in constructing this mock?
Edit:
Looks like this:
with open('x') as f:
f.read()
and this:
f = open('x')
f.read()
are different objects. Using the mock as a context manager makes it return a new Mock, whereas calling it directly returns whatever I've defined in mock_open.return_value. Any ideas?
This sounds like a good use-case for a StringIO object that already implements the file interface. Maybe you can make a file_mock = MagicMock(spec=file, wraps=StringIO('test')). Or you could just have your function accept a file-like object and pass it a StringIO instead of a real file, avoiding the need for ugly monkey-patching.
Have you looked the mock documentation?