Gem::QueryUtils#check_installed_gems

# File tmp/rubies/ruby-3.1.3/lib/rubygems/query_utils.rb, line 74
def check_installed_gems(gem_names)
  exit_code = 0

  if args.empty? && !gem_name?
    alert_error "You must specify a gem name"
    exit_code = 4
  elsif gem_names.count > 1
    alert_error "You must specify only ONE gem!"
    exit_code = 4
  else
    installed = installed?(gem_names.first, options[:version])
    installed = !installed unless options[:installed]

    say(installed)
    exit_code = 1 if !installed
  end

  exit_code
end