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/services/follow_service_spec.rb

@@ -7,7 +7,7 @@ RSpec.describe FollowService, type: :service do
 
   context 'local account' do
     describe 'locked account' do
-      let(:bob) { Fabricate(:user, email: 'bob@example.com', account: Fabricate(:account, locked: true, username: 'bob')).account }
+      let(:bob) { Fabricate(:account, locked: true, username: 'bob') }
 
       before do
         subject.call(sender, bob)
@@ -19,7 +19,7 @@ RSpec.describe FollowService, type: :service do
     end
 
     describe 'locked account, no reblogs' do
-      let(:bob) { Fabricate(:user, email: 'bob@example.com', account: Fabricate(:account, locked: true, username: 'bob')).account }
+      let(:bob) { Fabricate(:account, locked: true, username: 'bob') }
 
       before do
         subject.call(sender, bob, reblogs: false)
@@ -31,7 +31,7 @@ RSpec.describe FollowService, type: :service do
     end
 
     describe 'unlocked account, from silenced account' do
-      let(:bob) { Fabricate(:user, email: 'bob@example.com', account: Fabricate(:account, username: 'bob')).account }
+      let(:bob) { Fabricate(:account, username: 'bob') }
 
       before do
         sender.touch(:silenced_at)
@@ -44,7 +44,7 @@ RSpec.describe FollowService, type: :service do
     end
 
     describe 'unlocked account, from a muted account' do
-      let(:bob) { Fabricate(:user, email: 'bob@example.com', account: Fabricate(:account, username: 'bob')).account }
+      let(:bob) { Fabricate(:account, username: 'bob') }
 
       before do
         bob.mute!(sender)
@@ -58,7 +58,7 @@ RSpec.describe FollowService, type: :service do
     end
 
     describe 'unlocked account' do
-      let(:bob) { Fabricate(:user, email: 'bob@example.com', account: Fabricate(:account, username: 'bob')).account }
+      let(:bob) { Fabricate(:account, username: 'bob') }
 
       before do
         subject.call(sender, bob)
@@ -71,7 +71,7 @@ RSpec.describe FollowService, type: :service do
     end
 
     describe 'unlocked account, no reblogs' do
-      let(:bob) { Fabricate(:user, email: 'bob@example.com', account: Fabricate(:account, username: 'bob')).account }
+      let(:bob) { Fabricate(:account, username: 'bob') }
 
       before do
         subject.call(sender, bob, reblogs: false)
@@ -84,7 +84,7 @@ RSpec.describe FollowService, type: :service do
     end
 
     describe 'already followed account' do
-      let(:bob) { Fabricate(:user, email: 'bob@example.com', account: Fabricate(:account, username: 'bob')).account }
+      let(:bob) { Fabricate(:account, username: 'bob') }
 
       before do
         sender.follow!(bob)
@@ -97,7 +97,7 @@ RSpec.describe FollowService, type: :service do
     end
 
     describe 'already followed account, turning reblogs off' do
-      let(:bob) { Fabricate(:user, email: 'bob@example.com', account: Fabricate(:account, username: 'bob')).account }
+      let(:bob) { Fabricate(:account, username: 'bob') }
 
       before do
         sender.follow!(bob, reblogs: true)
@@ -110,7 +110,7 @@ RSpec.describe FollowService, type: :service do
     end
 
     describe 'already followed account, turning reblogs on' do
-      let(:bob) { Fabricate(:user, email: 'bob@example.com', account: Fabricate(:account, username: 'bob')).account }
+      let(:bob) { Fabricate(:account, username: 'bob') }
 
       before do
         sender.follow!(bob, reblogs: false)
@@ -124,7 +124,7 @@ RSpec.describe FollowService, type: :service do
   end
 
   context 'remote ActivityPub account' do
-    let(:bob) { Fabricate(:user, account: Fabricate(:account, username: 'bob', domain: 'example.com', protocol: :activitypub, inbox_url: 'http://example.com/inbox')).account }
+    let(:bob) { Fabricate(:account, username: 'bob', domain: 'example.com', protocol: :activitypub, inbox_url: 'http://example.com/inbox') }
 
     before do
       stub_request(:post, "http://example.com/inbox").to_return(:status => 200, :body => "", :headers => {})