DEV: Prefabrication (test optimization) (#7414)

* Introduced fab!, a helper that creates database state for a group

It's almost identical to let_it_be, except:

 1. It creates a new object for each test by default,
 2. You can disable it using PREFABRICATION=0

spec/components/validators/post_validator_spec.rb

@@ -4,7 +4,7 @@ require 'rails_helper'
 require_dependency 'validators/post_validator'
 
 describe Validators::PostValidator do
-  let(:topic) { Fabricate(:topic) }
+  fab!(:topic) { Fabricate(:topic) }
   let(:post) { build(:post, topic: topic) }
   let(:validator) { Validators::PostValidator.new({}) }
 
@@ -26,8 +26,8 @@ describe Validators::PostValidator do
     end
 
     describe "when post's topic is a PM between a human and a non human user" do
-      let(:robot) { Fabricate(:user, id: -3) }
-      let(:user) { Fabricate(:user) }
+      fab!(:robot) { Fabricate(:user, id: -3) }
+      fab!(:user) { Fabricate(:user) }
 
       let(:topic) do
         Fabricate(:private_message_topic, topic_allowed_users: [
@@ -189,8 +189,8 @@ describe Validators::PostValidator do
   end
 
   describe "unique_post_validator" do
-    let(:user) { Fabricate(:user, id: 999) }
-    let(:post) { Fabricate(:post, user: user, topic: topic) }
+    fab!(:user) { Fabricate(:user, id: 999) }
+    fab!(:post) { Fabricate(:post, user: user, topic: topic) }
 
     before do
       SiteSetting.unique_posts_mins = 5
@@ -240,9 +240,9 @@ describe Validators::PostValidator do
 
   context "force_edit_last_validator" do
 
-    let(:user) { Fabricate(:user) }
-    let(:other_user) { Fabricate(:user) }
-    let(:topic) { Fabricate(:topic) }
+    fab!(:user) { Fabricate(:user) }
+    fab!(:other_user) { Fabricate(:user) }
+    fab!(:topic) { Fabricate(:topic) }
 
     before do
       SiteSetting.max_consecutive_replies = 2

spec/components/validators/upload_validator_spec.rb

@@ -7,7 +7,7 @@ describe Validators::UploadValidator do
   subject(:validator) { described_class.new }
 
   describe 'validate' do
-    let(:user) { Fabricate(:user) }
+    fab!(:user) { Fabricate(:user) }
     let(:filename) { "discourse.csv" }
     let(:csv_file) { file_from_fixtures(filename, "csv") }
 
@@ -57,7 +57,7 @@ describe Validators::UploadValidator do
     end
 
     describe 'upload for site settings' do
-      let(:user) { Fabricate(:admin) }
+      fab!(:user) { Fabricate(:admin) }
 
       let(:upload) do
         Fabricate.build(:upload,
@@ -85,7 +85,7 @@ describe Validators::UploadValidator do
       end
 
       describe 'for normal user' do
-        let(:user) { Fabricate(:user) }
+        fab!(:user) { Fabricate(:user) }
 
         it 'should not allow the upload' do
           expect(subject.validate(upload)).to eq(nil)

spec/components/validators/username_setting_validator_spec.rb

@@ -21,8 +21,8 @@ describe UsernameSettingValidator do
     end
 
     context "regex support" do
-      let!(:darthvader) { Fabricate(:user, username: 'darthvader') }
-      let!(:luke) { Fabricate(:user, username: 'luke') }
+      fab!(:darthvader) { Fabricate(:user, username: 'darthvader') }
+      fab!(:luke) { Fabricate(:user, username: 'luke') }
 
       it "returns false if regex doesn't match" do
         v = described_class.new(regex: 'darth')