Coverage analysis under rails 8 beta seems to not be working

[gnarfle]

I recently updated an app to the rails 8 beta to play around with it and found the simplecov analysis reports a lot of missing code coverage. Attached is an example of a controller where the rails 7 version has 100% coverage and the rails 8 version says a lot of coverage is missing. These controllers are slightly reworked but the baffling part to me is that the rails 8 version declares I'm missing coverage for things like @user = User.new and params.permit not to mention saving the user, and I definitely have request specs and feature specs covering new and create here that get me 100% coverage in the rails version.

[Cosmo]

We have the same issue.
As a quick workaround, we disabled parallelize(workers: :number_of_processors) in test/test_helper.rb.

[Dandush03]

here is my file, it's working fine with parallelize processes

#=> test/test_helper.rb
# frozen_string_literal: true

ENV['RAILS_ENV'] ||= 'test'

require_relative 'supports/simplecov'
require_relative '../config/environment'
require 'rails/test_help'

module ActiveSupport
  class TestCase
    I18n.locale = :en
    # Run tests in parallel with specified workers

    parallelize_setup do |_worker|
      SimpleCov.command_name "Job::#{Process.pid}" if const_defined?(:SimpleCov)
    end

    parallelize(workers: :number_of_processors)

    # Setup all fixtures in test/fixtures/*.yml for all tests in alphabetical order.
    fixtures :all

    # Add more helper methods to be used by all tests here...
  end
end

#=> test/supports/simplecov.rb
# frozen_string_literal: true

require 'simplecov'

Rake.respond_to?(:application) &&
  Rake.application.respond_to?(:top_level_tasks) &&
  Rake.application.top_level_tasks.any? { |e| e.eql?('test:prepare') }

FileUtils.rm_f('coverage/.resultset.json')

SimpleCov.minimum_coverage 100
SimpleCov.start(:rails) do
  add_filter do |source_file|
    removed_lines = 0
    relevant_lines = source_file.src.count do |line|
      line = line.strip # remove leading and trailing whitespaces
      next if line.empty? # skip empty lines
      next if line.start_with?('#') # skip comments
      next removed_lines += 1 if line.start_with?('class', 'module') # skip class, module declarations
      next if line == 'end' # skip ends

      true
    end
    relevant_lines -= removed_lines
    relevant_lines <= 1
  end

  add_filter 'vendor/gems'
  add_filter 'preview/'

  at_exit do
    SimpleCov.formatter = SimpleCov::Formatter::SimpleFormatter
    SimpleCov.result.format!
  end
end