Use default worker/dispatcher only when the configuration is empty

That is, if there is some configuration not empty, do not fill missing
dispatcher or worker with the default. Just assume no
working/dispatching.

Author: rosa

lib/solid_queue/configuration.rb

@@ -55,15 +55,19 @@ def config_from(file_or_hash, env: Rails.env)
       end
 
       def workers_options
-        @workers_options ||= (raw_config[:workers] || [ WORKER_DEFAULTS ])
+        @workers_options ||= options_from_raw_config(:workers, WORKER_DEFAULTS)
           .map { |options| options.dup.symbolize_keys }
       end
 
       def dispatchers_options
-        @dispatchers_options ||= (raw_config[:dispatchers] || [ DISPATCHER_DEFAULTS ])
+        @dispatchers_options ||= options_from_raw_config(:dispatchers, DISPATCHER_DEFAULTS)
           .map { |options| options.dup.symbolize_keys }
       end
 
+      def options_from_raw_config(key, defaults)
+        raw_config.empty? ? [ defaults ] : Array(raw_config[key])
+      end
+
       def parse_recurring_tasks(tasks)
         Array(tasks).map do |id, options|
           Dispatcher::RecurringTask.from_configuration(id, **options)

test/unit/configuration_test.rb

@@ -36,6 +36,11 @@ class ConfigurationTest < ActiveSupport::TestCase
     assert_equal 2, configuration.workers.count
     assert_equal [ "background" ], configuration.workers.flat_map(&:queues).uniq
     assert_equal [ 10 ], configuration.workers.map(&:polling_interval).uniq
+
+    config_as_hash = { workers: [ background_worker, background_worker ] }
+    configuration = SolidQueue::Configuration.new(load_from: config_as_hash)
+    assert_empty configuration.dispatchers
+    assert_equal 2, configuration.workers.count
   end
 
   test "max number of threads" do