project_spec.rb

require 'spec_helper'

describe Project do

  describe 'nested attributes' do
    before do

      json = {
        "title" => "My Amazing Project",
        "skills_attributes" => [
          { "name" => "Ruby" },
          { "name" => "AJAX" },
          { "name" => "Backbone" }
        ]
      }

      @project = Project.new(json)
    end

    it "should have filled in all the skills" do
      @project.skills.length.should eq(3)
      @project.skills.first.name.should eq("Ruby")
    end

    it "should give me a hash with as_json" do
      @project.as_json.class.should eq(Hash)
    end

    it "should give me a string with to_json" do
      @project.to_json.class.should eq(String)
    end

  end

end

projects_controller_spec.rb

require 'spec_helper'

describe ProjectsController do
  before do
    @user = User.make!
  end

  describe 'POST to create' do
    before do
      json = Project.make(:user => @user).as_json.merge({
        :skills_attributes => ([Skill.make] * 3).as_json
      })
      json.delete :skills

      post :create, :project => json, :user_id => @user.id
    end

    it "should work" do
      expect(response).to be_success
    end

    it "should create a project and some skills" do
      expect(Project.count).to eq(1)
      expect(Skill.count).to eq(3)
    end

    it "should assign the skills to its proejct" do
      assigns(:project).skills.length.should eq(3)
    end
  end

end