Extract Pidfile setup and deletion to a different concern

Also, rename SupervisorTest to ForkSupervisorTest, as that's the one
being tested there.

Author: rosa

lib/solid_queue/supervisor/fork_supervisor.rb

@@ -2,10 +2,7 @@
 
 module SolidQueue
   class Supervisor::ForkSupervisor < Supervisor
-    include Signals
-
-    before_boot :setup_pidfile
-    after_shutdown :delete_pidfile
+    include Signals, Single
 
     def initialize(*)
       super
@@ -98,16 +95,6 @@ def replace_fork(pid, status)
         end
       end
 
-      def setup_pidfile
-        if path = SolidQueue.supervisor_pidfile
-          @pidfile = Pidfile.new(path).tap(&:setup)
-        end
-      end
-
-      def delete_pidfile
-        @pidfile&.delete
-      end
-
       def all_forks_terminated?
         forks.empty?
       end

lib/solid_queue/supervisor/single.rb

@@ -0,0 +1,25 @@
+# frozen_string_literal: true
+
+module SolidQueue
+  class Supervisor
+    module Single
+      extend ActiveSupport::Concern
+
+      included do
+        before_boot :setup_pidfile
+        after_shutdown :delete_pidfile
+      end
+
+      private
+        def setup_pidfile
+          if path = SolidQueue.supervisor_pidfile
+            @pidfile = Pidfile.new(path).tap(&:setup)
+          end
+        end
+
+        def delete_pidfile
+          @pidfile&.delete
+        end
+    end
+  end
+end

test/unit/supervisor_test.rb renamed to test/unit/fork_supervisor_test.rb

@@ -1,6 +1,6 @@
 require "test_helper"
 
-class SupervisorTest < ActiveSupport::TestCase
+class ForkSupervisorTest < ActiveSupport::TestCase
   self.use_transactional_tests = false
 
   setup do