test "validate username" do
    valid_usernames = %w[aa fifteencharonly]
    valid_usernames.each do |valid_username|
      @user.username = valid_username
      assert @user.valid?, "#{valid_username.inspect} should be valid"
    end
  end

  test "detect invalid username" do
    invalid_usernames = %w[a asdfjklasdfjkl16]
    invalid_usernames.each do |invalid_username|
      @user.username = invalid_username
      assert_not @user.valid?, "#{invalid_username.inspect}"
    end
  end