class RSpec::Core::Configuration

def mock_with(framework)

- called after verify_mocks_for_rspec (even if there are errors)
teardown_mocks_for_rspec

when expectations fail
- called after each example. Framework should raise an exception
verify_mocks_for_rspec

- called before each example
setup_mocks_for_rspec

should adhere to RSpec's mock framework adapter API:
Given a Module, includes that module in every example group. The module

mocking framework to save a little bit of overhead.
Given :nothing, configures no framework. Use this if you don't use any

framework.
Given any of :rspec, :mocha, :flexmock, or :rr, configures the named

`framework` can be a Symbol or a Module.

Sets the mock framework adapter module. 
def mock_with(framework)
  framework_module = case framework
  when Module
    framework
  when String, Symbol
    require case framework.to_s
            when /rspec/i
              'rspec/core/mocking/with_rspec'
            when /mocha/i
              'rspec/core/mocking/with_mocha'
            when /rr/i
              'rspec/core/mocking/with_rr'
            when /flexmock/i
              'rspec/core/mocking/with_flexmock'
            else
              'rspec/core/mocking/with_absolutely_nothing'
            end
    RSpec::Core::MockFrameworkAdapter
  end
  new_name, old_name = [framework_module, @mock_framework].map do |mod|
    mod.respond_to?(:framework_name) ?  mod.framework_name : :unnamed
  end
  unless new_name == old_name
    assert_no_example_groups_defined(:mock_framework)
  end
  @mock_framework = framework_module
end