create_topics_spec.rb

require 'spec_helper'

describe "CreateTopics" do
  it "creates topics" do
    @forum = Forum.create(name: 'Ruby')
    visit new_forum_topic_path, @forum.slug

    fill_in "Name", with: "Test"
    click_button "Submit"
  end
end

gistfile1.txt

Failure/Error: visit new_forum_topic_path, @forum.slug
     ActionController::UrlGenerationError:
       No route matches {:action=>"new", :controller=>"topics"} missing required keys: [:forum_id]