Add tests for pre-existing unix paths

1. test_binder.rb - test_pre_existing_unix

2. test_integration_cluster.rb - test_pre_existing_unix

test/test_binder.rb

@@ -78,6 +78,23 @@ class TestBinder < TestBinderBase
     assert_parsing_logs_uri [:tcp, :unix]
   end
 
+  def test_pre_existing_unix
+    skip UNIX_SKT_MSG unless UNIX_SKT_EXIST
+    unix_path = "test/#{name}_server.sock"
+
+    File.open(unix_path, mode: 'wb') { |f| f.puts 'pre eixisting' }
+    @binder.parse ["unix://#{unix_path}"], @events
+
+    assert_match %r!unix://#{unix_path}!, @events.stdout.string
+
+    refute_includes @binder.instance_variable_get(:@unix_paths), unix_path
+
+  ensure
+    if UNIX_SKT_EXIST
+      File.unlink unix_path if File.exist? unix_path
+    end
+  end
+
   private
 
   def assert_parsing_logs_uri(order = [:unix, :tcp])

test/test_integration_cluster.rb

@@ -12,7 +12,25 @@ class TestIntegrationCluster < TestIntegration
   end
 
   def teardown
-    super if HAS_FORK
+    return if skipped?
+    super
+  end
+
+  def test_pre_existing_unix
+    skip UNIX_SKT_MSG unless UNIX_SKT_EXIST
+
+    File.open(@bind_path, mode: 'wb') { |f| f.puts 'pre eixisting' }
+
+    cli_server "-w #{WORKERS} -t 0:6 -q test/rackup/sleep_step.ru", unix: :unix
+
+    stop_server
+
+    assert File.exist?(@bind_path)
+
+  ensure
+    if UNIX_SKT_EXIST
+      File.unlink @bind_path if File.exist? @bind_path
+    end
   end
 
   def test_siginfo_thread_print