Refactor and improve tests (#17386)

* Change account and user fabricators to simplify and improve tests

- `Fabricate(:account)` implicitly fabricates an associated `user` if
  no `domain` attribute is given (an account with `domain: nil` is
  considered a local account, but no user record was created), unless
  `user: nil` is passed
- `Fabricate(:account, user: Fabricate(:user))` should still be possible
  but is discouraged.

* Fix and refactor tests

- avoid passing unneeded attributes to `Fabricate(:user)` or
  `Fabricate(:account)`
- avoid embedding `Fabricate(:user)` into a `Fabricate(:account)` or the other
  way around
- prefer `Fabricate(:user, account_attributes: …)` to
  `Fabricate(:user, account: Fabricate(:account, …)`
- also, some tests were using remote accounts with local user records, which is
  not representative of production code.

spec/models/account_spec.rb

@@ -17,7 +17,7 @@ RSpec.describe Account, type: :model do
       end
 
       context 'when the account is of a local user' do
-        let!(:subject) { Fabricate(:account, user: Fabricate(:user, email: 'foo+bar@domain.org')) }
+        let!(:subject) { Fabricate(:user, email: 'foo+bar@domain.org').account }
 
         it 'creates a canonical domain block' do
           subject.suspend!

spec/models/admin/account_action_spec.rb

@@ -5,8 +5,8 @@ RSpec.describe Admin::AccountAction, type: :model do
 
   describe '#save!' do
     subject              { account_action.save! }
-    let(:account)        { Fabricate(:account, user: Fabricate(:user, admin: true)) }
-    let(:target_account) { Fabricate(:account, user: Fabricate(:user)) }
+    let(:account)        { Fabricate(:user, admin: true).account }
+    let(:target_account) { Fabricate(:account) }
     let(:type)           { 'disable' }
 
     before do

spec/models/public_feed_spec.rb

@@ -31,7 +31,6 @@ RSpec.describe PublicFeed, type: :model do
     end
 
     it 'filters out silenced accounts' do
-      account = Fabricate(:account)
       silenced_account = Fabricate(:account, silenced: true)
       status = Fabricate(:status, account: account)
       silenced_status = Fabricate(:status, account: silenced_account)
@@ -176,8 +175,7 @@ RSpec.describe PublicFeed, type: :model do
 
       context 'with language preferences' do
         it 'excludes statuses in languages not allowed by the account user' do
-          user = Fabricate(:user, chosen_languages: [:en, :es])
-          @account.update(user: user)
+          @account.user.update(chosen_languages: [:en, :es])
           en_status = Fabricate(:status, language: 'en')
           es_status = Fabricate(:status, language: 'es')
           fr_status = Fabricate(:status, language: 'fr')
@@ -188,8 +186,7 @@ RSpec.describe PublicFeed, type: :model do
         end
 
         it 'includes all languages when user does not have a setting' do
-          user = Fabricate(:user, chosen_languages: nil)
-          @account.update(user: user)
+          @account.user.update(chosen_languages: nil)
 
           en_status = Fabricate(:status, language: 'en')
           es_status = Fabricate(:status, language: 'es')
@@ -199,7 +196,8 @@ RSpec.describe PublicFeed, type: :model do
         end
 
         it 'includes all languages when account does not have a user' do
-          expect(@account.user).to be_nil
+          @account.update(user: nil)
+
           en_status = Fabricate(:status, language: 'en')
           es_status = Fabricate(:status, language: 'es')
 

spec/models/user_spec.rb

@@ -194,12 +194,12 @@ RSpec.describe User, type: :model do
     end
 
     it "returns 'private' if user has not configured default privacy setting and account is locked" do
-      user = Fabricate(:user, account: Fabricate(:account, locked: true))
+      user = Fabricate(:account, locked: true).user
       expect(user.setting_default_privacy).to eq 'private'
     end
 
     it "returns 'public' if user has not configured default privacy setting and account is not locked" do
-      user = Fabricate(:user, account: Fabricate(:account, locked: false))
+      user = Fabricate(:account, locked: false).user
       expect(user.setting_default_privacy).to eq 'public'
     end
   end
@@ -248,7 +248,7 @@ RSpec.describe User, type: :model do
 
   it_behaves_like 'Settings-extended' do
     def create!
-      User.create!(account: Fabricate(:account), email: 'foo@mastodon.space', password: 'abcd1234', agreement: true)
+      User.create!(account: Fabricate(:account, user: nil), email: 'foo@mastodon.space', password: 'abcd1234', agreement: true)
     end
 
     def fabricate