Use phantomjs gem to demonstrate phantomjs is a dependency, and autoinstall phantomjs.

Gemfile

@@ -130,6 +130,7 @@ group :test do
   gem 'capybara'
   gem 'database_cleaner'
   gem 'poltergeist'
+  gem 'phantomjs', :require => 'phantomjs/poltergeist'
   # Set of rails validations matchers to describe models
   gem 'shoulda'
   # Extracted from RSpec 3 stub_model and mock_model

Gemfile.lock

@@ -241,6 +241,7 @@ GEM
       ast (>= 1.1, < 3.0)
       slop (~> 3.4, >= 3.4.5)
     pdf-core (0.2.5)
+    phantomjs (1.9.7.1)
     poltergeist (1.5.1)
       capybara (~> 2.1)
       cliver (~> 0.3.1)
@@ -443,6 +444,7 @@ DEPENDENCIES
   omniauth-openid
   paper_trail
   paperclip
+  phantomjs
   poltergeist
   prawn_rails
   protected_attributes

spec/spec_helper.rb

@@ -19,6 +19,7 @@ ActiveRecord::Migration.maintain_test_schema!
 
 # Add poltergeist to use it as JS driver
 require 'capybara/poltergeist'
+require 'phantomjs'
 
 # Requires supporting ruby files with custom matchers and macros, etc, in
 # spec/support/ and its subdirectories. Files matching `spec/**/*_spec.rb` are
@@ -65,7 +66,7 @@ RSpec.configure do |config|
   Capybara.javascript_driver = :poltergeist
 
   Capybara.register_driver :poltergeist do |app|
-    Capybara::Poltergeist::Driver.new(app, js_errors: false)
+    Capybara::Poltergeist::Driver.new(app, phantomjs: Phantomjs.path, js_errors: false)
   end
 
   # Includes helpers and connect them to specific types of tests