```ruby
require 'prometheus/client'
require 'prometheus/client/support/unicorn'

Prometheus::Client.configure do |config|
  config.logger = Rails.logger

  config.initial_mmap_file_size = 4 * 1024
  config.multiprocess_files_dir = ENV['prometheus_multiproc_dir']

  if Rails.env.development? || Rails.env.test?
    config.multiprocess_files_dir ||= Rails.root.join('tmp/prometheus_multiproc_dir')
  end

  config.pid_provider = Prometheus::Client::Support::Unicorn.method(:worker_pid_provider)
end

Gitlab::Application.configure do |config|
  # 0 should be Sentry to catch errors in this middleware
  config.middleware.insert(1, Gitlab::Metrics::RequestsRackMiddleware)
end

Sidekiq.configure_server do |config|
  config.on(:startup) do
    Gitlab::Metrics::SidekiqMetricsExporter.instance.start
  end
end

if Gitlab::Metrics.prometheus_metrics_enabled?
  unless Sidekiq.server?
    Gitlab::Metrics::Samplers::UnicornSampler.initialize_instance(Settings.monitoring.unicorn_sampler_interval).start
  end

  Gitlab::Metrics::Samplers::RubySampler.initialize_instance(Settings.monitoring.ruby_sampler_interval).start
end
```

Disable the background Prometheus sampler in tests
user
```ruby
require 'prometheus/client'
require 'prometheus/client/support/unicorn'

Prometheus::Client.configure do |config|
  config.logger = Rails.logger

  config.initial_mmap_file_size = 4 * 1024
  config.multiprocess_files_dir = ENV['prometheus_multiproc_dir']

  if Rails.env.development? || Rails.env.test?
    config.multiprocess_files_dir ||= Rails.root.join('tmp/prometheus_multiproc_dir')
  end

  config.pid_provider = Prometheus::Client::Support::Unicorn.method(:worker_pid_provider)
end

Gitlab::Application.configure do |config|
  # 0 should be Sentry to catch errors in this middleware
  config.middleware.insert(1, Gitlab::Metrics::RequestsRackMiddleware)
end

Sidekiq.configure_server do |config|
  config.on(:startup) do
    Gitlab::Metrics::SidekiqMetricsExporter.instance.start
  end
end

if !Rails.env.test? && Gitlab::Metrics.prometheus_metrics_enabled?
  unless Sidekiq.server?
    Gitlab::Metrics::Samplers::UnicornSampler.initialize_instance(Settings.monitoring.unicorn_sampler_interval).start
  end

  Gitlab::Metrics::Samplers::RubySampler.initialize_instance(Settings.monitoring.ruby_sampler_interval).start
end
```
assistant