Patches

The testlayer supports patches which can be used to mock out any modules that are used inside a tornado application.

Here is an example of a tornado application that uses the os modules listdir method:

>>> import json
>>> class ListDirHandler(RequestHandler):
...     def get(self):
...         import os
...         return self.write(json.dumps(os.listdir('.')))

>>> my_app = Application(handlers=[(r'/', ListDirHandler)], debug=True)

Now define the fake listdir method:

>>> def fake_listdir(path):
...     return ['fake_file']

Create the monkey patch:

>>> from unittest.mock import patch
>>> listdir_patch = patch('os.listdir', fake_listdir)

Create the test layer using the patch:

>>> tornado_layer = TornadoLayer(my_app, port=None, patches=[listdir_patch])
>>> tornado_layer.setUp()

>>> url = 'http://localhost:{}/'.format(tornado_layer.port)
>>> f = urlopen(url)
>>> f.read()
b'["fake_file"]'

>>> f.close()
>>> tornado_layer.tearDown()