Use VCR to record HTTP responses and replay them using fakeweb.
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VCR provides helpers to record HTTP requests for URIs that are not registered with fakeweb, and replay them later. It works with any ruby testing framework and provides built-in support for cucumber.


gem install vcr


This README assumes you are familiar with FakeWeb; if not, please checkout the README.

VCR was inspired by NetRecorder, but was designed from the ground up to support localized recording and replaying, rather than the global recording and replaying of NetRecorder. In general, I believe that tests should not rely upon anything global. You're coupling your test to something outside of it that may later change and break the test. It's far better to localize things to each test, as much as possible. VCR, in combination with FakeWeb, makes it easy to do this with the recording and replying of HTTP responses.


Cassettes are central to the way VCR works. They are a similar to VHS cassettes–your library of cassettes is your library of previously recorded responses that can be replayed. When you create a cassette, it does the following:

  • It loads the previously recorded responses from the cache file corresponding to the cassette name.

  • It register these responses with fakeweb (depending on the cassette's :record option–see below)

  • It sets the FakeWeb.allow_net_connect setting based on the cassette's :record option.

While a cassette is active, any HTTP requests to a URL of a previously recorded response will use the recorded response. New HTTP requests (i.e. HTTP requests that have not been previously recorded) will be recorded to the same cache file, depending on your :record option. When you destroy a cassette, it does the following:

  • It saves all of the recorded responses (both old and new) to a cached yml file corresponding to the cassette name.

  • It removes the registrations it made with fakeweb, to prevent “leakage” into other tests.

  • It reverts the FakeWeb.allow_net_connect back to whatever it was before the cassette was created.

Record modes

VCR supports 3 record modes, which configure when it records new responses. You can set a default record mode in your configuration (see below) and a per-cassette record mode when creating a cassette. The record modes are:

  • :all - This will cause VCR to re-record all HTTP requests that occur. When the cassette is created, it will not register any of the cached responses with fakeweb. FakeWeb.allow_net_connect will be set to true, so it can record the requests. Use this when you want to re-record all of the HTTP requests for a cassette. Alternately, you can simply delete the corresponding cache file and use the :unregistered record mode, described below.

  • :none - This will prevent VCR from recording, or even allowing, any new HTTP requests. The previously recorded responses will be registered with fakeweb. FakeWeb.allow_net_connect will be set to false, so that no new HTTP connections are allowed. Use this when you want to guarantee that no external HTTP requests will be made while the given cassette is active. Fakeweb will raise an error in this case.

  • :unregistered - This will use the previously recorded responses, and record any new requests that are not registered with fakeweb. The previously recorded responses will be registered with fakeweb. FakeWeb.allow_net_connect will be set to true, so that VCR will record any new HTTP requests within the cassette. Use this when it's ok for external HTTP requests to be made without you explicitly allowing it. New requests will get saved to the cassettes yml file, and automatically get used in the future.


require 'vcr'

# Set the default allow_net_connect option--usually you'll want this off.
# You don't usually want your test suite to make HTTP connections, do you?
FakeWeb.allow_net_connect = false

VCR.config do |c|
  # the cache_dir is where the cassette yml files will be saved.
  c.cache_dir = File.join(Rails.root, 'features', 'fixtures', 'vcr_cassettes')

  # this record mode will be used for any cassette you create without specifying a record mode.
  c.default_cassette_record_mode = :none

This can go pretty much wherever, as long as this code is run before your tests, specs or scenarios. I tend to put it in spec/support/vcr.rb, test/support/vcr.rb or features/support/vcr.rb.

Usage with your favorite test/spec framework

VCR can easily be used with any ruby test or spec framework. Usually, you'll want to use VCR.with_cassette:

VCR.with_cassette('geocoding/Seattle, WA', :record => :unregistered) do
  # do something that causes an HTTP request.

Alternately, you can create and destroy the cassette with individual method calls from setup/before and teardown/after:

describe "Something that makes an HTTP request" do
  before(:each) do
    VCR.create_cassette!('geocoding/Seattle, WA', :record => :unregistered)

  it "should do something that makes an HTTP request"

  after(:each) do

In both of these cases, VCR would use the file geocoding/Seattle_WA.yml within the configured cache dir. The :record setting is optional–if you leave it blank, your configured default will be used.

Usage with Cucumber

VCR provides special support for cucumber. You can of course use VCR.with_cassette within a step definition, and that's the recommended way for any of your step definitions. But many times I find myself using generic step definitions provided by another library (such as the webrat/capybara web steps generated by cucumber-rails), and I don't want to modify these. VCR provides cucumber tagging support to help in these cases.

First, tag your scenario with something descriptive:

Scenario: Sign up with facebook connect

Then let VCR know about this tag, in features/support/vcr.rb (or some similar support file):

VCR.cucumber_tags do |t|
  t.tags '@facebook_http_request', '@twitter_status_update', :record => :none
  t.tags '@another_scenario_tag'   # the default record mode will be used for this tag.

For each of the tags you specify in your cucumber_tags block, VCR will set up the appropriate Before and After hooks to use a cassette for the entire scenario. The tag (minus the '@') will be used as the cassette name, and it'll go in the cucumber_tags subdirectory of the configured cache dir.

Suggested Workflow

First, configure VCR and FakeWeb as I have above. I like setting FakeWeb.allow_net_connect to false and VCR's default_cassette_record_mode to :none so that no new HTTP requests are made without me explicitly allowing it.

When an HTTP request is made, you'll get an error from FakeWeb, such as:

FakeWeb::NetConnectNotAllowedError: Real HTTP connections are disabled. Unregistered request: get

Find the place that is making the HTTP request (the backtrace should help here). If you've already recorded this HTTP request to a cassette from a different test, you can simply re-use the cassette. Use VCR.with_cassette, as shown above. You may also want to refactor this into a helper method that sets up the VCR cassette and does whatever makes the HTTP request:

def set_user_address(user, address, city, state)
  VCR.with_cassette("geocoding/#{address}, #{city}, #{state}", :record => :unregistered) do
    user.address.update_attributes!(:address => address, :city => city, :state => state)

In this case, I've used a dynamic cassette name based on the address being geocoded. That way, each separate address gets a different cassette, and tests that set the same user address will reuse the same cassette. I've also set the record mode to :unregistered so that VCR will automatically record geocoding requests for a new address to a new cassette, without me having to do anything.

If the HTTP request that triggered the error is new, you'll have to record it for the first time. Simply use VCR.with_cassette with the record mode set to :unregistered or :all. Run the test again, and VCR will record the HTTP response. I usually remove the record mode at this point so that it uses the default of :none in the future. Future test runs will use the recorded response, and if your code changes so that it is making a new HTTP request, you'll get the same FakeWeb error as shown above.

Ruby Version Compatibility

specs.should pass if RUBY_VERSION =~ /^1.(8.6|8.7|9.1)$/

Notes, etc.

  • The cassette name determines the name of the cache file for the given cassette. Strings or symbols are fine, and you can include any characters, but spaces and invalid file name characters will be removed before the cassette reads or writes to the file.

  • You can use a directory separator (i.e. '/') in your cassette names to cause it to use a subdirectory of the cache_dir. The cucumber tagging support uses this.

  • VCR maintains a simple stack of cassettes. This allows you to nest them as deeply as you want. This is particularly useful when you have a cucumber step definition that uses a cassette, and you also want to use a cassette for the entire scenario using the tagging support.

Note on Patches/Pull Requests

  • Fork the project.

  • Make your feature addition or bug fix.

  • Add tests for it. This is important so I don't break it in a future version unintentionally.

  • Commit, do not mess with rakefile, version, or history. (if you want to have your own version, that is fine but bump version in a commit by itself I can ignore when I pull)

  • Send me a pull request. Bonus points for topic branches.



Copyright © 2010 Myron Marston. See LICENSE for details.