prefer create_request, use StringIO over custom slice operators

spec/lib/rex/post/meterpreter/packet_parser_spec.rb

@@ -1,33 +1,21 @@
 # -*- coding:binary -*-
 require 'rex/post/meterpreter/packet'
 require 'rex/post/meterpreter/packet_parser'
-
+require 'stringio'
 
 RSpec.describe Rex::Post::Meterpreter::PacketParser do
   subject(:parser){
     Rex::Post::Meterpreter::PacketParser.new
   }
   before(:example) do
-    @req_packt = Rex::Post::Meterpreter::Packet.new(
-          Rex::Post::Meterpreter::PACKET_TYPE_REQUEST,
-          "test_method")
-    @raw = @req_packt.to_r
-    @sock = double('Socket')
-    allow(@sock).to receive(:read) do |arg|
-      @raw.slice!(0,arg)
-    end
-  end
-
-  it "should initialise with expected defaults" do
-    expect(parser.send(:raw)).to eq ""
-    expect(parser.send(:hdr_length_left)).to eq 12
-    expect(parser.send(:payload_length_left)).to eq 0
+    @request_packet = Rex::Post::Meterpreter::Packet.create_request("test_method")
+    @sock = StringIO.new(@request_packet.to_r)
   end
 
   it "should parse valid raw data into a packet object" do
-    while @raw.length >0
+    begin
       parsed_packet = parser.recv(@sock)
-    end
+    end while parsed_packet.nil?
     expect(parsed_packet).to be_a Rex::Post::Meterpreter::Packet
     expect(parsed_packet.type).to eq Rex::Post::Meterpreter::PACKET_TYPE_REQUEST
     expect(parsed_packet.method?("test_method")).to eq true