Usage¶
import vcr
import urllib.request
with vcr.use_cassette('fixtures/vcr_cassettes/synopsis.yaml'):
response = urllib.request.urlopen('http://www.iana.org/domains/reserved').read()
assert b'Example domains' in response
Run this test once, and VCR.py will record the HTTP request to
fixtures/vcr_cassettes/synopsis.yaml
. Run it again, and VCR.py will
replay the response from iana.org when the http request is made. This
test is now fast (no real HTTP requests are made anymore), deterministic
(the test will continue to pass, even if you are offline, or iana.org
goes down for maintenance) and accurate (the response will contain the
same headers and body you get from a real request).
You can also use VCR.py as a decorator. The same request above would look like this:
@vcr.use_cassette('fixtures/vcr_cassettes/synopsis.yaml')
def test_iana():
response = urllib.request.urlopen('http://www.iana.org/domains/reserved').read()
assert b'Example domains' in response
When using the decorator version of use_cassette
, it is possible to
omit the path to the cassette file.
@vcr.use_cassette()
def test_iana():
response = urllib.request.urlopen('http://www.iana.org/domains/reserved').read()
assert b'Example domains' in response
In this case, the cassette file will be given the same name as the test function, and it will be placed in the same directory as the file in which the test is defined. See the Automatic Test Naming section below for more details.
Record Modes¶
VCR supports 4 record modes (with the same behavior as Ruby’s VCR):
once¶
Replay previously recorded interactions.
Record new interactions if there is no cassette file.
Cause an error to be raised for new requests if there is a cassette file.
It is similar to the new_episodes record mode, but will prevent new, unexpected requests from being made (e.g. because the request URI changed).
once is the default record mode, used when you do not set one.
new_episodes¶
Record new interactions.
Replay previously recorded interactions. It is similar to the once record mode, but will always record new interactions, even if you have an existing recorded one that is similar, but not identical.
This was the default behavior in versions < 0.3.0
none¶
Replay previously recorded interactions.
Cause an error to be raised for any new requests. This is useful when your code makes potentially dangerous HTTP requests. The none record mode guarantees that no new HTTP requests will be made.
all¶
Record new interactions.
Never replay previously recorded interactions. This can be temporarily used to force VCR to re-record a cassette (i.e. to ensure the responses are not out of date) or can be used when you simply want to log all HTTP requests.
Unittest Integration¶
Inherit from VCRTestCase
for automatic recording and playback of HTTP
interactions.
from vcr.unittest import VCRTestCase
import requests
class MyTestCase(VCRTestCase):
def test_something(self):
response = requests.get('http://example.com')
Similar to how VCR.py returns the cassette from the context manager,
VCRTestCase
makes the cassette available as self.cassette
:
self.assertEqual(len(self.cassette), 1)
self.assertEqual(self.cassette.requests[0].uri, 'http://example.com')
By default cassettes will be placed in the cassettes
subdirectory next to the
test, named according to the test class and method. For example, the above test
would read from and write to cassettes/MyTestCase.test_something.yaml
The configuration can be modified by overriding methods on your subclass:
_get_vcr_kwargs
, _get_cassette_library_dir
and _get_cassette_name
.
To modify the VCR
object after instantiation, for example to add a matcher,
you can hook on _get_vcr
, for example:
class MyTestCase(VCRTestCase):
def _get_vcr(self, **kwargs):
myvcr = super(MyTestCase, self)._get_vcr(**kwargs)
myvcr.register_matcher('mymatcher', mymatcher)
myvcr.match_on = ['mymatcher']
return myvcr
See the source for the default implementations of these methods.
If you implement a setUp
method on your test class then make sure to call
the parent version super().setUp()
in your own in order to continue getting
the cassettes produced.
VCRMixin¶
In case inheriting from VCRTestCase
is difficult because of an existing
class hierarchy containing tests in the base classes, inherit from VCRMixin
instead.
from vcr.unittest import VCRMixin
import requests
import unittest
class MyTestMixin(VCRMixin):
def test_something(self):
response = requests.get(self.url)
class MyTestCase(MyTestMixin, unittest.TestCase):
url = 'http://example.com'
Pytest Integration¶
A Pytest plugin is available here : pytest-vcr.
Alternative plugin, that also provides network access blocking: pytest-recording.