explaining usage for let block in rspec tests

let_example.rb

RSpec.describe UsersController, type: :controller do
  # let can be used as instance variables, instead of @user
  let(:create_user) { FactoryGirl.create(:user) }
  let(:new_path){ new_user_path }
  let(:edit_path){ edit_user_path }
  # let can be used as parameters that can be shared across examples
  let(:create_params){  
    {
      name: "NAME",
      age: "20"
    }
  }
  
  describe "POST #create" do
    context "with valid parameters" do
      before(:each) do
        post :create, create_params
      end
      it {  should respond_with(200) }
      it "should return valid JSON response" do
        response_body = JSON.parse(response.body)
        expect(response_body[:data][:name]).to eq(create_params[:name])
      end
    end
  end
end