#VCR.py

This is a Python version of Ruby's VCR library.

##What it does Simplify and speed up testing HTTP by recording all HTTP interactions and saving them to "cassette" files, which are yaml files containing the contents of your requests and responses. Then when you run your tests again, they all just hit the text files instead of the internet. This speeds up your tests and lets you work offline.

If the server you are testing against ever changes its API, all you need to do is delete your existing cassette files, and run your tests again. All of the mocked responses will be updated with the new API.

##Compatibility Notes This should work with Python 2.6 and 2.7, and pypy.

Currently I've only tested this with urllib2, urllib3, and requests. It's known to NOT WORK with urllib.

##How to use it

import vcr
import urllib2

with vcr.use_cassette('fixtures/vcr_cassettes/synopsis.yaml'):
    response = urllib2.urlopen('http://www.iana.org/domains/reserved').read()
    assert 'Example domains' in response

Run this test once, and VCR.py will record the http request to fixtures/vcr_cassettes/synopsis.yml. 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).

If you don't like VCR's defaults, you can set options by instantiating a VCR class and setting the options on it.

import vcr

my_vcr = vcr.VCR(
    serializer = 'json',
    cassette_library_dir = 'fixtures/cassettes',
    record_mode = 'once',
    match_on = ['url', 'method'],
)

with my_vcr.use_cassette('test.json'):
    # your http code here

Otherwise, you can override options each time you use a cassette.

with vcr.use_cassette('test.yml', serializer='json', record_mode='once'):
    # your http code here

Note: Per-cassette overrides take precedence over the global config.

Request matching is configurable and allows you to change which requests VCR considers identical. The default behavior is ['url', method'] which means that requests with both the same URL and method (ie POST or GET) are considered identical.

This can be configured by changing the match_on setting.

The following options are available :

• method (for example, POST or GET)
• url (the full URL, including the protocol)
• host (the hostname of the server receiving the request)
• path (excluding the hostname)
• body (the entire request body)
• headers (the headers of the request)

If these options don't work for you, you can also register your own request matcher. This is described in the Advanced section of this README.

VCR supports 4 record modes (with the same behavior as Ruby's VCR):

• 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 (i.e. because the request URI changed).

once is the default record mode, used when you do not set one.

• 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

• 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.

• 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.

If you want, VCR.py can return information about the cassette it is using to record your requests and responses. This will let you record your requests and responses and make assertions on them, to make sure that your code under test is generating the expected requests and responses. This feature is not present in Ruby's VCR, but I think it is a nice addition. Here's an example:

import vcr
import urllib2

with vcr.use_cassette('fixtures/vcr_cassettes/synopsis.yaml') as cass:
    response = urllib2.urlopen('http://www.zombo.com/').read()
    # cass should have 1 request inside it
    assert len(cass) == 1 
    # the request url should have been http://www.zombo.com/
    assert cass.requests[0].url == 'http://www.zombo.com/'

The Cassette object exposes the following properties which I consider part of the API. The fields are as follows:

• requests: A list of vcr.Request objects containing the requests made while this cassette was being used, ordered by the order that the request was made.
• responses: A list of the responses made.
• play_count: The number of times this cassette has had a response played back
• play_counts: A collections.Counter showing the number of times each response has been played back, indexed by the request
• response_of(request): Access the response for a given request.

The Request object has the following properties

• URL: The full url of the request, including the protocol. Example: "http://www.google.com/"
• path: The path of the request. For example "/" or "/home.html"
• host: The host of the request, for example "www.google.com"
• port: The port the request was made on
• method : The method used to make the request, for example "GET" or "POST"
• protocol: The protocol used to make the request (http or https)
• body: The body of the request, usually empty except for POST / PUT / etc

Don't like JSON or YAML? That's OK, VCR.py can serialize to any format you would like. Create your own module or class instance with 2 methods:

• def deserialize(cassette_string)
• def serialize(cassette_dict)

Finally, register your class with VCR to use your new serializer.

import vcr

BogoSerializer(object):
    """
    Must implement serialize() and deserialize() methods
    """
    pass

my_vcr = vcr.VCR()
my_vcr.register_serializer('bogo', BogoSerializer())

with my_vcr.use_cassette('test.bogo', serializer='bogo'):
    # your http here

# After you register, you can set the default serializer to your new serializer

my_vcr.serializer = 'bogo'

with my_vcr.use_cassette('test.bogo'):
    # your http here

Create your own method with the following signature

def my_matcher(r1, r2):

Your method receives the two requests and must return True if they match, False if they don't.

Finally, register your method with VCR to use your new request matcher.

import vcr

def jurassic_matcher(r1, r2):
    return r1.url == r2.url and 'JURASSIC PARK' in r1.body

my_vcr = vcr.VCR()
my_vcr.register_matcher('jurassic', jurassic_matcher)

with my_vcr.use_cassette('test.yml', match_on=['jurassic']):
    # your http here

# After you register, you can set the default match_on to use your new matcher

my_vcr.match_on = ['jurassic']

with my_vcr.use_cassette('test.yml'):
    # your http here

##Installation

VCR.py is a package on PyPI, so you can pip install vcrpy (first you may need to brew install libyaml [Homebrew])

##Ruby VCR compatibility I'm not trying to match the format of the Ruby VCR YAML files. Cassettes generated by Ruby's VCR are not compatible with VCR.py.

##Known Issues This library is a work in progress, so the API might change on you. There are probably some bugs floating around too.

##Changelog

• 0.3.5: Fix compatibility with requests 2.x
• 0.3.4: Bugfix: close file before renaming it. This fixes an issue on Windows. Thanks @smallcode for the fix.
• 0.3.3: Bugfix for error message when an unreigstered custom matcher was used
• 0.3.2: Fix issue with new config syntax and the match_on parameter. Thanks, @chromy!
• 0.3.1: Fix issue causing full paths to be sent on the HTTP request line.
• 0.3.0: Backwards incompatible release - Added support for record modes, and changed the default recording behavior to the "once" record mode. Please see the documentation on record modes for more. Added support for custom request matching, and changed the default request matching behavior to match only on the URL and method. Also, improved the httplib mocking to add support for the HTTPConnection.send() method. This means that requests won't actually be sent until the response is read, since I need to record the entire request in order to match up the appropriate response. I don't think this should cause any issues unless you are sending requests without ever loading the response (which none of the standard httplib wrappers do, as far as I know. Thanks to @fatuhoku for some of the ideas and the motivation behind this release.
• 0.2.1: Fixed missing modules in setup.py
• 0.2.0: Added configuration API, which lets you configure some settings on VCR (see the README). Also, VCR no longer saves cassettes if they haven't changed at all and supports JSON as well as YAML (thanks @sirpengi). Added amazing new skeumorphic logo, thanks @hairarrow.
• 0.1.0: backwards incompatible release - delete your old cassette files:
  This release adds the ability to access the cassette to make assertions on it, as well as a major code refactor thanks to @dlecocq. It also fixes a couple longstanding bugs with redirects and HTTPS. [#3 and #4]
• 0.0.4: If you have libyaml installed, vcrpy will use the c bindings instead. Speed up your tests! Thanks @dlecocq
• 0.0.3: Add support for requests 1.2.3. Support for older versions of requests dropped (thanks @vitormazzi and @bryanhelmig)
• 0.0.2: Add support for requests / urllib3
• 0.0.1: Initial Release

##Similar libraries in Python Neither of these really implement the API I want, but I have cribbed some code from them.

• https://github.com/bbangert/Dalton
• https://github.com/storborg/replaylib

These were created after I created VCR.py but do something similar:

• https://github.com/gabrielfalcao/HTTPretty
• https://github.com/kanzure/python-requestions
• https://github.com/uber/cassette

#License This library uses the MIT license. See LICENSE.txt for more details