I'm currently trying to mock out the open() built in method in Python for a test. However, I always end up getting a crash and this resulting message:
File "/opt/home/venv/lib/python2.7/site-packages/nose-1.3.0-py2.7.egg/nose/result.py", line 187, in _exc_info_to_string
return _TextTestResult._exc_info_to_string(self, err, test)
File "/opt/python-2.7.3/lib/python2.7/unittest/result.py", line 164, in _exc_info_to_string
msgLines = traceback.format_exception(exctype, value, tb)
File "/opt/python-2.7.3/lib/python2.7/traceback.py", line 141, in format_exception
list = list + format_tb(tb, limit)
File "/opt/python-2.7.3/lib/python2.7/traceback.py", line 76, in format_tb
return format_list(extract_tb(tb, limit))
File "/opt/python-2.7.3/lib/python2.7/traceback.py", line 101, in extract_tb
line = linecache.getline(filename, lineno, f.f_globals)
File "/opt/home/venv/lib/python2.7/linecache.py", line 14, in getline
lines = getlines(filename, module_globals)
File "/opt/home/venv/lib/python2.7/linecache.py", line 40, in getlines
return updatecache(filename, module_globals)
File "/opt/home/venv/lib/python2.7/linecache.py", line 127, in updatecache
with open(fullname, 'rU') as fp:
AttributeError: __exit__
Here is my test code:
m = mox.Mox()
m.StubOutWithMock(__builtin__, 'open')
mock_file = m.CreateMock(__builtin__.file)
open(mox.IgnoreArg(), mox.IgnoreArg()).AndReturn(mock_file)
mock_file.write(mox.IgnoreArg()).MultipleTimes()
mock_file.close()
write_file_method()
__exit__
is the method that gets called when you try to close a file. Your mock file does not handle mock_file.close()
, just open()
. You'll need to mock the close
method too.
Edit:
On second though, why do you want to mock open
? AFAIK you shouldn't be doing that method. The method under test should take an open stream (instead of a filename, for instance). In production code, clients are responsible for opening a file (e.g. pickle.dump
). In your tests, you pass in a StringIO
, or a mock object that supports writing.
Edit 2: I would split your method in two and test each bit separately.
StringIO
and write to that, so your tests can then verify the correct thing has been written.