title: RSpec MustBeConfiguredBeforeExampleGroupsError on plain project
body: <p>I'm setting up a Rails 3.1 project and like to properly test it using RSpec.</p>
  
  <p>After running <code>rails g rspec:install</code> and further running <code>rspec</code>, the console messages read as follows:</p>
  
  <pre><code>% rspec
  /Library/Ruby/Gems/1.8/gems/rspec-core-2.7.0/lib/rspec/core/configuration.rb:470:in `assert_no_example_groups_defined': RSpec's mock_framework configuration option must be configured before any example groups are defined, but you have already defined a group. (RSpec::Core::Configuration::MustBeConfiguredBeforeExampleGroupsError)
      from /Library/Ruby/Gems/1.8/gems/rspec-core-2.7.0/lib/rspec/core/configuration.rb:168:in `mock_framework='
      from /Library/Ruby/Gems/1.8/gems/rspec-core-2.7.0/lib/rspec/core/configuration.rb:142:in `mock_with'
      from /Users/ened/project/spec/controllers/../spec_helper.rb:19
      from /Library/Ruby/Gems/1.8/gems/rspec-core-2.7.0/lib/rspec/core.rb:71:in `configure'
      from /Users/ened/project/spec/controllers/../spec_helper.rb:11
      from /Library/Ruby/Gems/1.8/gems/activesupport-3.1.0/lib/active_support/dependencies.rb:240:in `require'
      from /Library/Ruby/Gems/1.8/gems/activesupport-3.1.0/lib/active_support/dependencies.rb:240:in `require'
      from /Library/Ruby/Gems/1.8/gems/activesupport-3.1.0/lib/active_support/dependencies.rb:225:in `load_dependency'
      from /Library/Ruby/Gems/1.8/gems/activesupport-3.1.0/lib/active_support/dependencies.rb:240:in `require'
      from /Users/ened/project/spec/controllers/submissions_controller_spec.rb:1
      from /Library/Ruby/Gems/1.8/gems/activesupport-3.1.0/lib/active_support/dependencies.rb:234:in `load'
      from /Library/Ruby/Gems/1.8/gems/activesupport-3.1.0/lib/active_support/dependencies.rb:234:in `load'
      from /Library/Ruby/Gems/1.8/gems/activesupport-3.1.0/lib/active_support/dependencies.rb:225:in `load_dependency'
      from /Library/Ruby/Gems/1.8/gems/activesupport-3.1.0/lib/active_support/dependencies.rb:234:in `load'
      from /Library/Ruby/Gems/1.8/gems/rspec-core-2.7.0/lib/rspec/core/configuration.rb:459:in `load_spec_files'
      from /Library/Ruby/Gems/1.8/gems/rspec-core-2.7.0/lib/rspec/core/configuration.rb:459:in `map'
      from /Library/Ruby/Gems/1.8/gems/rspec-core-2.7.0/lib/rspec/core/configuration.rb:459:in `load_spec_files'
      from /Library/Ruby/Gems/1.8/gems/rspec-core-2.7.0/lib/rspec/core/command_line.rb:18:in `run'
      from /Library/Ruby/Gems/1.8/gems/rspec-core-2.7.0/lib/rspec/core/runner.rb:80:in `run_in_process'
      from /Library/Ruby/Gems/1.8/gems/rspec-core-2.7.0/lib/rspec/core/runner.rb:69:in `run'
      from /Library/Ruby/Gems/1.8/gems/rspec-core-2.7.0/lib/rspec/core/runner.rb:10:in `autorun'
      from /usr/bin/rspec:19
  </code></pre>
  
  <p>My <code>rspec/spec_helper.rb</code> looks like this:</p>
  
  <pre><code># This file is copied to spec/ when you run 'rails generate rspec:install'
  ENV["RAILS_ENV"] ||= 'test'
  require File.expand_path("../../config/environment", __FILE__)
  require 'rspec/rails'
  require 'rspec/autorun'
  
  # Requires supporting ruby files with custom matchers and macros, etc,
  # in spec/support/ and its subdirectories.
  Dir[Rails.root.join("spec/support/**/*.rb")].each {|f| require f}
  
  RSpec.configure do |config|
    # == Mock Framework
    #
    # If you prefer to use mocha, flexmock or RR, uncomment the appropriate line:
    #
    # config.mock_with :mocha
    # config.mock_with :flexmock
    # config.mock_with :rr
    config.mock_with :rspec
  
    # Remove this line if you're not using ActiveRecord or ActiveRecord fixtures
    config.fixture_path = "#{::Rails.root}/spec/fixtures"
  
    # If you're not using ActiveRecord, or you'd prefer not to run each of your
    # examples within a transaction, remove the following line or assign false
    # instead of true.
    config.use_transactional_fixtures = true
  
    # If true, the base class of anonymous controllers will be inferred
    # automatically. This will be the default behavior in future versions of
    # rspec-rails.
    config.infer_base_class_for_anonymous_controllers = false
  end
  </code></pre>
  
  <p>I thought it's configured already using the config.mock_with ? I'm puzzled, what is missing?</p>