Use a reserved port to test for a non-existing TCP server

* Avoids a race between finding an available port and another process starting a server on it.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@58747 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

spec/rubyspec/library/socket/fixtures/classes.rb

@@ -46,6 +46,11 @@ module SocketSpecs
     find_available_port
   end
 
+  def self.reserved_unused_port
+    # https://en.wikipedia.org/wiki/List_of_TCP_and_UDP_port_numbers
+    0
+  end
+
   def self.sockaddr_in(port, host)
     Socket::SockAddr_In.new(Socket.sockaddr_in(port, host))
   end

spec/rubyspec/library/socket/tcpsocket/shared/new.rb

@@ -8,7 +8,7 @@ describe :tcpsocket_new, shared: true do
 
   it "refuses the connection when there is no server to connect to" do
     lambda do
-      TCPSocket.send(@method, SocketSpecs.hostname, SocketSpecs.local_port)
+      TCPSocket.send(@method, SocketSpecs.hostname, SocketSpecs.reserved_unused_port)
     end.should raise_error(Errno::ECONNREFUSED)
   end