Remove flatware config block, re-extract simplecov config to standalone file (#39017)

.simplecov

@@ -0,0 +1,26 @@
+# frozen_string_literal: true
+
+SimpleCov.start 'rails' do
+  # During parallel runs, ensure unique names for post-run merge
+  command_name "job-#{ENV['TEST_ENV_NUMBER']}" if ENV['TEST_ENV_NUMBER']
+
+  if ENV['CI']
+    require 'simplecov-lcov'
+    formatter SimpleCov::Formatter::LcovFormatter
+    formatter.config.report_with_single_file = true
+  else
+    formatter SimpleCov::Formatter::HTMLFormatter
+  end
+
+  enable_coverage :branch
+
+  add_filter 'lib/linter'
+
+  add_group 'Libraries', 'lib'
+  add_group 'Policies', 'app/policies'
+  add_group 'Presenters', 'app/presenters'
+  add_group 'Search', 'app/chewy'
+  add_group 'Serializers', 'app/serializers'
+  add_group 'Services', 'app/services'
+  add_group 'Validators', 'app/validators'
+end

spec/rails_helper.rb

@@ -2,40 +2,7 @@
 
 ENV['RAILS_ENV'] ||= 'test'
 
-if ENV.fetch('COVERAGE', false)
-  require 'simplecov'
-
-  SimpleCov.start 'rails' do
-    # During parallel runs, ensure unique names for post-run merge
-    command_name "job-#{ENV['TEST_ENV_NUMBER']}" if ENV['TEST_ENV_NUMBER']
-
-    if ENV['CI']
-      require 'simplecov-lcov'
-      formatter SimpleCov::Formatter::LcovFormatter
-      formatter.config.report_with_single_file = true
-    else
-      formatter SimpleCov::Formatter::HTMLFormatter
-    end
-
-    enable_coverage :branch
-
-    add_filter 'lib/linter'
-
-    add_group 'Libraries', 'lib'
-    add_group 'Policies', 'app/policies'
-    add_group 'Presenters', 'app/presenters'
-    add_group 'Search', 'app/chewy'
-    add_group 'Serializers', 'app/serializers'
-    add_group 'Services', 'app/services'
-    add_group 'Validators', 'app/validators'
-  end
-
-  if defined?(Flatware)
-    Flatware.configure do |config|
-      config.after_fork { |test| SimpleCov.at_fork.call(test) } # Combines parallel coverage results
-    end
-  end
-end
+require 'simplecov' if ENV.fetch('COVERAGE', false)
 
 # This needs to be defined before Rails is initialized
 STREAMING_PORT = ENV.fetch('TEST_STREAMING_PORT', '4020')