Approval Tests for Ruby
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Approvals are based on the idea of the golden master.

You take a snapshot of an object, and then compare all future versions of the object to the snapshot.

Big hat tip to Llewellyn Falco who developed the approvals concept, as well as the original approvals libraries (.NET, Java, Ruby, PHP, probably others).

See ApprovalTests for videos and additional documentation about the general concept.

Also, check out Herding Code's podcast #117 in which Llewellyn Falco is interviewed about approvals.


Approvals.configure do |config|
  config.approvals_path = 'output/goes/here/'

The default location for the output files is



Approvals.verify(your_subject, :format => :json)

This will raise an ApprovalError in the case of a failure.

The first time the approval is run, a file will be created with the contents of the subject of your approval:

the_name_of_the_approval.received.txt # or .json, .html, .xml as appropriate

Since you have not yet approved anything, the *.approved file does not exist, and the comparison will fail.

Customizing formatted output

The default writer uses the :to_s method on the subject to generate the output for the received file. For custom complex objects you will need to provide a custom writer to get helpful output, rather than the default:

#<Object:0x0000010105ea40> # or whatever the object id is

Create a custom writer class somewhere accessible to your test:

class MyCustomWriter < Approvals::Writers::TextWriter
  def format(data)
    # Custom data formatting here

  def filter(data)
    # Custom data filtering here

In your test, use a string to reference your custom class:

it "verifies a complex object" do
  Approvals.verify hello, :format => "MyCustomWriter"

Define and use different custom writers as needed!


The gem comes with a command-line tool that makes it easier to manage the *.received.* and *.approved.* files.

The basic usage is:

approvals verify

This goes through each approval failure in turn showing you the diff.

The option --diff or -d configures which difftool to use (for example opendiff, vimdiff, etc). The default value is diff.

The option --ask or -a, which after showing you a diff will offer to approve the received file (move it from *.received.* to *.approved.*.). The default is true. If you set this to false, then nothing happens beyond showing you the diff, and you will need to rename files manually.

Workflow Using VimDiff

I have the following mapped to <leader>v in my .vimrc file:

map <leader>v :!approvals verify -d vimdiff -a<cr>

I tend to run my tests from within vim with an on-the-fly mapping:

:map Q :wa <Bar> :!ruby path/to/test_file.rb<cr>

When I get one or more approval failures, I hit <leader>v. This gives me the vimdiff.

When I've inspected the result, I hit :qa which closes both sides of the diff.

Then I'm asked if I want to approve the received file [yN]. If there are multiple diffs, this handles each failure in turn.


For the moment the only direct integration is with RSpec.

require 'approvals/rspec'

The default directory for output files when using RSpec is


You can override this:

RSpec.configure do |config|
  config.approvals_path = 'some/other/path'

The basic format of the approval is modeled after RSpec's it:

it 'works' do
  verify do
    'this is the the thing you want to verify'


When using RSpec, the namer is set for you, using the example's full_description.

Approvals.verify(thing, :name => 'the name of your test')


You can pass a format for your output before it gets written to the file. At the moment, only text, xml, html, and json are supported, while text is the default.

Simply add a :format => :text, :format => :xml, :format => :html, or :format => :json option to the example:

page = '<html><head></head><body><h1>ZOMG</h1></body></html>'
Approvals.verify page, :format => :html

data = '{\'beverage\':\'coffee\'}'
Approvals.verify data, :format => :json

In RSpec, it looks like this:

verify :format => :html do

verify :format => :json do

If you like you could also change the default format globally with:

RSpec.configure do |config|
  config.approvals_default_format = :json # or :xml, :html

Exclude dynamically changed values from json

Approvals.configure do |config|
  config.excluded_json_keys = {
    :id =>/(\A|_)id$/,
    :date => /_at$/

It will replace values with placeholders:

{id: 5, created_at: "2013-08-29 13:48:08 -0700"}


{id: "<id>", created_at: "<date>"}

Approving a spec

If the contents of the received file is to your liking, you can approve the file by renaming it.

For an example who's full description is My Spec:

mv my_spec.received.txt my_spec.approved.txt

When you rerun the approval, it should now pass.

Expensive computations

The Executable class allows you to perform expensive operations only when the command to execute it changes.

For example, if you have a SQL query that is very slow, you can create an executable with the actual SQL to be performed.

The first time the spec runs, it will fail, allowing you to inspect the results. If this output looks right, approve the query. The next time the spec is run, it will compare only the actual SQL.

If someone changes the query, then the comparison will fail. Both the previously approved command and the received command will be executed so that you can inspect the difference between the results of the two.

executable = do |output|
  # do something on failure

Approvals.verify(executable, :options => :here)

RSpec executable

There is a convenience wrapper for RSpec that looks like so:

verify do
  executable(subject.slow_sql) do |command|
     result = ActiveRecord::Base.connection.execute(command)
     # do something to display the result

Copyright (c) 2011 Katrina Owen, released under the MIT license