In addition to these specific assertions, you also have easy access to various collections that the regular test/unit assertions can be used against. These collections are:

  • assigns: Instance variables assigned in the action that are available for the view.

  • session: Objects being saved in the session.

  • flash: The flash objects currently in the session.

  • cookies: Cookies being sent to the user on this request.

These collections can be used just like any other hash:

assert_not_nil assigns(:person) # makes sure that a @person instance variable was set
assert_equal "Dave", cookies[:name] # makes sure that a cookie called :name was set as "Dave"
assert flash.empty? # makes sure that there's nothing in the flash

For historic reasons, the assigns hash uses string-based keys. So assigns won’t work, but assigns will. To appease our yearning for symbols, though, an alternative accessor has been deviced using a method call instead of index referencing. So assigns(:person) will work just like assigns, but again, assigns will not work.

On top of the collections, you have the complete url that a given action redirected to available in redirect_to_url.

For redirects within the same controller, you can even call follow_redirect and the redirect will be followed, triggering another action call which can then be asserted against.

Manipulating the request collections

The collections described above link to the response, so you can test if what the actions were expected to do happened. But sometimes you also want to manipulate these collections in the incoming request. This is really only relevant for sessions and cookies, though. For sessions, you just do:

@request.session[:key] = "value"

For cookies, you need to manually create the cookie, like this:

@request.cookies["key"] = CGI::Cookie.new("key", "value")

Testing named routes

If you’re using named routes, they can be easily tested using the original named routes methods straight in the test case. Example:

assert_redirected_to page_url(:title => 'foo')
Namespace
Methods
C
I
Included Modules
Constants
NO_STRIP = %w{pre script style textarea}
 
Class Public methods
included(klass)

Source: show 

# File rails/actionpack/lib/action_controller/assertions.rb, line 47
def self.included(klass)
  klass.class_eval do
    include ActionController::Assertions::ResponseAssertions
    include ActionController::Assertions::SelectorAssertions
    include ActionController::Assertions::RoutingAssertions
    include ActionController::Assertions::TagAssertions
    include ActionController::Assertions::DomAssertions
    include ActionController::Assertions::ModelAssertions
    include ActionController::Assertions::DeprecatedAssertions
  end
end
Instance Public methods
clean_backtrace(&block)

Source: show 

# File rails/actionpack/lib/action_controller/assertions.rb, line 59
def clean_backtrace(&block)
  yield
rescue Test::Unit::AssertionFailedError => e         
  path = File.expand_path(__FILE__)
  raise Test::Unit::AssertionFailedError, e.message, e.backtrace.reject { |line| File.expand_path(line) =~ %r#{path}/ }
end