devise/test/support/assertions_helper.rb

class ActiveSupport::TestCase
  def assert_not(assertion)
    assert !assertion
  end

  def assert_blank(assertion)
    assert assertion.blank?
  end

  def assert_not_blank(assertion)
    assert !assertion.blank?
  end
  alias :assert_present :assert_not_blank

  def assert_email_sent(&block)
    assert_difference('ActionMailer::Base.deliveries.size') { yield }
  end

  def assert_email_not_sent(&block)
    assert_no_difference('ActionMailer::Base.deliveries.size') { yield }
  end

  # Execute the block setting the given values and restoring old values after
  # the block is executed.
  def swap(object, new_values)
    old_values = {}
    new_values.each do |key, value|
      old_values[key] = object.send key
      object.send :"#{key}=", value
    end
    yield
  ensure
    old_values.each do |key, value|
      object.send :"#{key}=", value
    end
  end
end