コミット＆マージの前にtestをパスできない！

railsチュートリアルの13章を進めています。
次の流れとしては、コミットとマージなのですが
$rails test　を行うとエラーが出て消えません。

「本番環境での画像アップロード」の項はスキップできる
と書いてあったのでスキップしました。

●以下エラー内容

Running via Spring preloader in process 10328
Started with run options --seed 48153

ERROR["test_successful_edit", UsersEditTest, 0.01050325799951679]
 test_successful_edit#UsersEditTest (0.01s)
NameError:         NameError: uninitialized constant Micropost::PictureUploader
            app/models/micropost.rb:4:in `<class:Micropost>'
            app/models/micropost.rb:1:in `<top (required)>'

 FAIL["test_micropost_interface", MicropostsInterfaceTest, 1.646527965000132]
 test_micropost_interface#MicropostsInterfaceTest (1.65s)
        "Micropost.count" didn't change by 0.
        Expected: 38
          Actual: 39
        test/integration/microposts_interface_test.rb:14:in `block in <class:MicropostsInterfaceTest>'

 FAIL["test_content_should_be_at_most_140_characters", MicropostTest, 1.8568898459998309]
 test_content_should_be_at_most_140_characters#MicropostTest (1.86s)
        Expected true to be nil or false
        test/models/micropost_test.rb:26:in `block in <class:MicropostTest>'

 FAIL["test_content_should_be_present", MicropostTest, 1.8622546129990951]
 test_content_should_be_present#MicropostTest (1.86s)
        Expected true to be nil or false
        test/models/micropost_test.rb:21:in `block in <class:MicropostTest>'

 FAIL["test_user_id_should_be_present", MicropostTest, 1.868930400998579]
 test_user_id_should_be_present#MicropostTest (1.87s)
        Expected true to be nil or false
        test/models/micropost_test.rb:16:in `block in <class:MicropostTest>'

  50/50: [======================] 100% Time: 00:00:01, Time: 00:00:01

Finished in 1.93830s
50 tests, 260 assertions, 4 failures, 1 errors, 0 skips

なんどもにらめっこしてみたのですが、いまだにどこでミスをしているのか
わかりません。。。
是非ともお力添えいただきたいです。

エラーメッセージに記載されているファイルを載せておきます。

【app/models/micropost.rb】

class Micropost < ApplicationRecord
  belongs_to :user
  default_scope -> { order(created_at: :desc) }
  mount_uploader :picture, PictureUploader
  validates :user_id, presence: true
  validates :content, presence: true, length: { maximum: 140 }
  validate  :picture_size

  private

    # アップロードされた画像のサイズをバリデーションする
    def picture_size
      if picture.size > 5.megabytes
        errors.add(:picture, "should be less than 5MB")
      end
    end
end

【test/integration/microposts_interface_test.rb】

require 'test_helper'

class MicropostsInterfaceTest < ActionDispatch::IntegrationTest

  def setup
    @user = users(:michael)
  end

  test "micropost interface" do
    log_in_as(@user)
    get root_path
    assert_select 'div.pagination'
    # 無効な送信
    assert_no_difference 'Micropost.count' do
      post microposts_path, params: { micropost: { content: "" } }
    end
    assert_select 'div#error_explanation'
    # 有効な送信
    content = "This micropost really ties the room together"
    assert_difference 'Micropost.count', 1 do
      post microposts_path, params: { micropost: { content: content } }
    end
    assert_redirected_to root_url
    follow_redirect!
    assert_match content, response.body
    # 投稿を削除する
    assert_select 'a', text: 'delete'
    first_micropost = @user.microposts.paginate(page: 1).first
    assert_difference 'Micropost.count', -1 do
      delete micropost_path(first_micropost)
    end
    # 違うユーザーのプロフィールにアクセス (削除リンクがないことを確認)
    get user_path(users(:archer))
    assert_select 'a', text: 'delete', count: 0
  end
end

【test/models/micropost_test.rb】

require 'test_helper'

class MicropostTest < ActiveSupport::TestCase

  def setup
    @user = users(:michael)
    @micropost = @user.microposts.build(content: "Lorem ipsum")
  end

  test "should be valid" do
    assert @micropost.valid?
  end

  test "user id should be present" do
    @micropost.user_id = nil
    assert_not @micropost.valid?
  end
  
  test "content should be present" do
    @micropost.content = "   "
    assert_not @micropost.valid?
  end

  test "content should be at most 140 characters" do
    @micropost.content = "a" * 141
    assert_not @micropost.valid?
  end
  
  test "order should be most recent first" do
    assert_equal microposts(:most_recent), Micropost.first
  end
end