note_handler.rb

module NoteHandler
  # params = { "new_tags"=>"People, Entrepreneurs ", "tag_list"=>"Ruby, Rails, ActiveRecord, " }
  # @note.add_tags(params[:new_tags], params[:tag_list])
  def add_tags(existing_tags, new_tags)
    tag_names = tag_names(existing_tags, new_tags)
    self.tags << tag_creator(tag_names)
  end

  def tag_names(existing_tags, new_tags)
    (existing_tags + new_tags.strip).split(", ")
  end

  def tag_creator(tag_names)
    tag_names.map { |name| collection.tags.find_or_create_by(name: name ) }
  end
end

note_handler_spec.rb

require 'spec_helper'

describe NoteHandler do
  let(:collection) { create(:collection) }
  let(:note) { create(:note, collection: collection ) }
  let(:tag1) { create(:tag, collection: collection) }
  let(:tag2) { create(:tag, collection: collection) }
  let(:new_tags) {" RSpec, Ruby "}
  let(:existing_tags) { "#{tag1.name}, #{tag2.name}, " }

  describe "#add_tags" do
    it "adds new and existing Tags to the Note" do
      note.add_tags(existing_tags, new_tags)

      expect(note.tags).to have(4).items
      expect(note.tags).to match_array(collection.tags)
    end
  end

  describe "#tag_names" do
    it "returns an array of new and existing Tag names" do
      expected_tags = (existing_tags + new_tags.strip).split(", ")
      actual_tags = note.tag_names(existing_tags, new_tags)

      expect(actual_tags).to eq expected_tags
    end
  end

  describe "#tag_creator" do
    it "returns existing Tags" do
      tags = note.tag_creator([tag1.name, tag2.name])

      expect(tags).to match_array(collection.tags)
    end

    it "creates new Tags" do
      tags = note.tag_creator(["Rails", "Ruby"])

      expect(tags).to match_array(collection.tags)
    end
  end
end

# Parameters: {"utf8"=>"✓", "authenticity_token"=>"H6tbVG+9aVXV3NYMztwHQEudsKKZ2fKnJPXI98ow1AE=", "note"=>{"title"=>"d