Rspec error, “undefined method 'downcase'

I keep getting this error when running my Rspec test and can't figure out why. I'm pretty new to Rails (and programming in general) so any direction or help would be much appreciated!

EDIT: Here is a link to the repo, if anyone would like to sift through it and/or replicate the error. https://github.com/FluxAnimus/sample_app/tree/sign-up

Failures:

1) User pages profile page 
 Failure/Error: before { visit user_path(user) }
 ActionView::Template::Error:
   undefined method `downcase' for nil:NilClass
 # ./app/helpers/users_helper.rb:5:in `gravatar_for'
 # ./app/views/users/show.html.erb:3:in `_app_views_users_show_html_erb__1766857043046396980_38603940'
 # ./spec/requests/user_pages_spec.rb:9:in `block (3 levels) in <top (required)>'

2) User pages profile page 
 Failure/Error: before { visit user_path(user) }
 ActionView::Template::Error:
   undefined method `downcase' for nil:NilClass
 # ./app/helpers/users_helper.rb:5:in `gravatar_for'
 # ./app/views/users/show.html.erb:3:in `_app_views_users_show_html_erb__1766857043046396980_38603940'
 # ./spec/requests/user_pages_spec.rb:9:in `block (3 levels) in <top (required)>'

Finished in 0.46129 seconds
39 examples, 2 failures

Failed examples:

rspec ./spec/requests/user_pages_spec.rb:12 # User pages profile page 
rspec ./spec/requests/user_pages_spec.rb:11 # User pages profile page

I'm in Chapter 7.13 of the Ruby on Rails tutorial. The tests cleared just fine until I added the Gravatar code and FactoryGirls Gem.

/app/helpers/users_helper.rb file

module UsersHelper

  # Returns the Gravatar (http://gravatar.com/) for the given user.
  def gravatar_for(user)
    gravatar_id = Digest::MD5::hexdigest(user.email.downcase)
    gravatar_url = "https://secure.gravatar.com/avatar/#{gravatar_id}"
    image_tag(gravatar_url, alt: user.name, class: "gravatar")
  end
end

spec/requests/user_pages_spec.rb

require 'spec_helper'

describe "User pages" do

  subject { page }

  describe "profile page" do
    let(:user) { FactoryGirl.create(:user) }
    before { visit user_path(user) }

    it { should have_content(user.name) }
    it { should have_title(user.name) }
  end
.
.
.
end

And the last reference: app/views/users/show.html.erb

<% provide(:title, @user.name) %>
<h1>
  <%= gravatar_for @user %>
  <%= @user.name %> 
</h1>

Here is the factory file:

FactoryGirl.define do
  factory :user do
    name     "Michael Hartl"
    email    "michael@example.com"
    password "foobar"
    password_confirmation "foobar"
  end
end

app/controllers/users_controller.rb

class UsersController < ApplicationController

    def show
        @user = User.find(params[:id])
    end

    def new
    end
end

回答1:

Assuming you're using the definition of gravatar_for in the tutorial, downcase is only referenced in the context of user.email.downcase which means that user is defined, but the email method/attribute of user returns nil. You can also go by the filename, method and line number provided in the stack trace to identifying the offending code.

Update: In your User model you, had a before_save call which included the following:

self.email = email.downcase!

Since downcase! returns nil, this has the effect of setting email to nil. Per the tutorial, you can use either of the following instead:

self.email.downcase!

or:

self.email = email.downcase

回答2:

You have a variable that you think is a string, but it's actually nil.

You can't call downcase on nil, so you're getting this error.

Welcome to Ruby, you'll be seeing that one a lot. :)

EDIT

I see you've added some code to the question.

As the error message says, it's user_helper.rb line 5:

gravatar_id = Digest::MD5::hexdigest(user.email.downcase)

It's user.email that is nil. I'm guessing that your FactoryGirl factory isn't assigning an email address to the user.