test "login with valid information followed by logout" do
  get login_path
  post login_path, session: { email: @user.email, password: 'password' }
  assert is_logged_in?
  assert_redirected_to @user
  follow_redirect!
  assert_template 'users/show'
  assert_select "a[href=?]", login_path, count: 0
  assert_select "a[href=?]", logout_path
  assert_select "a[href=?]", user_path(@user)
  delete logout_path
  assert_redirected_to root_url
  assert_not is_logged_in? # <-- this line is the one that cocks up.
  follow_redirect!
  assert_select "a[href=?]", login_path
  assert_select "a[href=?]", logout_path,      count: 0
  assert_select "a[href=?]", user_path(@user), count: 0
end

def destroy
  logout
  redirect_to root_url
end

def logout
  session.delete(:user_id)
  @current_user = nil
end

def is_logged_in?
  !current_user.nil?
end

test "login with invalid information" do
  get login_path
  assert_template 'sessions/new'
  post login_path, session: { email: "", password: "" }
  assert_template 'sessions/new'
  assert_not flash.empty?
  get root_path
  assert flash.empty?
end