Supress devise flash messages

sessions_controller_spec.rb

require 'rails_helper'

RSpec.describe Devise::SessionsController, :type => :controller do
  before(:each) do
    @request.env["devise.mapping"] = Devise.mappings[:user]
  end

  def action
    post :create
  end

  context "action filtered" do
    controller do
      self.supress_devise_flash = :create

      def create
        set_flash_message(:notice, "message")
        render text: "hello world"
      end
    end

    before { action }

    it { should_not set_the_flash }
  end

  context "action not filtered" do
    controller do
      self.supress_devise_flash = []

      def create
        set_flash_message(:notice, "message")
        render text: "hello world"
      end
    end

    before { action }

    it { should set_the_flash }
  end

  context "filtered non existent action" do
    controller do
      self.supress_devise_flash = [:update]

      def create
        set_flash_message(:notice, "message")
        render text: "hello world"
      end
    end

    before { action }

    it { should set_the_flash }
  end
end

some_initializer.rb

Devise::SessionsController.supress_devise_flash = :create, :destroy

supress_devise_flash_message.rb

module SupressDeviseFlashMessage
  extend ActiveSupport::Concern

  included do
    class_attribute :supress_devise_flash, instance_accessor: false
    self.supress_devise_flash = []

    def set_flash_message_with_supress(*args)
      set_flash_message_without_supress(*args) unless Array.wrap(self.class.supress_devise_flash).include?(params[:action].to_sym)
    end

    alias_method_chain :set_flash_message, :supress
  end
end

DeviseController.send(:include, SupressDeviseFlashMessage)