RSpec::Snapshot

Adds snapshot testing to RSpec, inspired by Jest.

Installation

Add this line to your application's Gemfile:

gem 'rspec-snapshot'

And then execute:

$ bundle install

Or install it yourself as:

$ gem install rspec-snapshot

Usage

The gem provides match_snapshot and snapshot RSpec matchers which take a snapshot name as an argument like:

# match_snapshot
expect(generated_email).to match_snapshot('welcome_email')

# match argument with snapshot
expect(logger).to have_received(:info).with(snapshot('log message'))

When a test is run using a snapshot matcher and a snapshot file does not exist matching the passed name, the test value encountered will be serialized and stored in your snapshot directory as the file: #{snapshot_name}.snap

When a test is run using a snapshot matcher and a snapshot file exists matching the passed name, then the test value encountered will be serialized and compared to the snapshot file contents. If the values match your test passes, otherwise it fails.

Rails request testing

RSpec.describe 'Posts', type: :request do
  describe 'GET /posts' do
    it 'returns a list of post' do
      get posts_path

      expect(response.body).to match_snapshot('get_posts')
    end
  end
end

Rails view testing

RSpec.describe 'widgets/index', type: :view do
  it 'displays all the widgets' do
    assign(:widgets, [
      Widget.create!(:name => 'slicer'),
      Widget.create!(:name => 'dicer')
    ])

    render

    expect(rendered).to match_snapshot('widgets/index')
  end
end

UPDATE_SNAPSHOTS environment variable

Occasionally you may want to regenerate all encountered snapshots for a set of tests. To do this, just set the UPDATE_SNAPSHOTS environment variable for your test command.

Update all snapshots

$ UPDATE_SNAPSHOTS=true bundle exec rspec

Update snapshots for some subset of tests

$ UPDATE_SNAPSHOTS=true bundle exec rspec spec/foo/bar

Configuration

Global configurations for rspec-snapshot are optional. Details below:

RSpec.configure do |config|
  # The default setting is `:relative`, which means snapshot files will be
  # created in a '__snapshots__' directory adjacent to the spec file where the
  # matcher is used.
  #
  # Set this value to put all snapshots in a fixed directory
  config.snapshot_dir = "spec/fixtures/snapshots"

  # Defaults to using the awesome_print gem to serialize values for snapshots
  #
  # Set this value to use a custom snapshot serializer
  config.snapshot_serializer = MyFavoriteSerializer
end

Custom serializers

By default, values to be stored as snapshots are serialized to human readable string form using the awesome_print gem.

You can pass custom serializers to rspec-snapshot if you prefer. Pass a serializer class name to the global RSpec config, or to an individual matcher as a config option:

# Set a custom serializer for all tests
RSpec.configure do |config|
  config.snapshot_serializer = MyCoolGeneralSerializer
end

# Set a custom serializer for this specific test
expect(html_response).to(
  match_snapshot('html_response', { snapshot_serializer: MyAwesomeHTMLSerializer })
)

Serializer classes are required to have one instance method dump which takes the value to be serialized and returns a string.

Migration

If you're updating to version 2.x.x from 1.x.x, you may need to update all your existing snapshots since the serialization method has changed.

$ UPDATE_SNAPSHOTS=true bundle exec rspec

Development

Initial Setup

Install a current version of ruby (> 2.5) and bundler. Then install gems

$ bundle install

Linting

$ bundle exec rubocop

Unit tests

$ bundle exec rspec

Interactive console with the gem code loaded

$ bin/console

Rake commands

To install this gem onto your local machine, run bundle exec rake install. To release a new version, update the version number in version.rb, and then run bundle exec rake release, which will create a git tag for the version, push git commits and tags, and push the .gem file to rubygems.org.

Contributing

Bug reports and pull requests are welcome on GitHub at https://github.com/levinmr/rspec-snapshot.

A big thanks to the original author @yesmeck.

rwx-research/rspec-snapshot