diff --git a/tests/flexnbd.rb b/tests/flexnbd.rb
index 94a0ebd..df70bc6 100644
--- a/tests/flexnbd.rb
+++ b/tests/flexnbd.rb
@@ -1,25 +1,151 @@
 require 'socket'
 require 'thread'
+require 'rexml/document'
+require 'rexml/streamlistener'
 
 Thread.abort_on_exception = true
 
+
+class Executor
+  attr_reader :pid
+
+  def run( cmd )
+    @pid = fork do exec @cmd end
+  end
+end # class Executor
+
+
+class ValgrindExecutor
+  attr_reader :pid
+
+  class Error
+    attr_accessor :what, :kind
+    attr_reader :backtrace
+    def initialize
+      @backtrace=[]
+      @what = ""
+      @kind = ""
+    end
+
+    def add_frame
+      @backtrace << {}
+    end
+
+    def add_fn(fn)
+      @backtrace.last[:fn] = fn
+    end
+
+    def add_file(file)
+      @backtrace.last[:file] = file
+    end
+
+    def add_line(line)
+      @backtrace.last[:line] = line
+    end
+
+    def to_s
+      ([@what + " (#{@kind})"] + @backtrace.map{|h| "#{h[:file]}:#{h[:line]} #{h[:fn]}" }).join("\n")
+    end
+
+  end # class Error
+
+
+  class ErrorListener
+    include REXML::StreamListener
+    def initialize( killer )
+      @killer = killer
+    end
+
+    def text( text )
+      @text = text
+    end
+
+    def tag_start(tag, attrs)
+      case tag.to_s
+      when "error"
+        @error = Error.new
+      when "frame"
+        @error.add_frame
+      end
+    end
+
+    def tag_end(tag)
+      case tag.to_s
+      when "what"
+        @error.what = @text if @error
+        @text = ""
+      when "kind"
+        @error.kind = @text if @error
+      when "file"
+        @error.add_file( @text ) if @error
+      when "fn"
+        @error.add_fn( @text ) if @error
+      when "line"
+        @error.add_line( @text ) if @error
+      when "error"
+        @killer.call( @error )
+      end
+    end
+  end # class ErrorListener
+
+
+  def initialize
+    @pid = nil
+  end
+
+  def run( cmd )
+    @io_r, io_w = IO.pipe
+    @pid = fork do exec( "valgrind --xml=yes --xml-fd=#{io_w.fileno} " + cmd ) end
+    launch_watch_thread( @pid, @io_r )
+    @pid
+  end
+
+
+  def call( err )
+    Process.kill( "KILL", @pid )
+    $stderr.puts "*"*72
+    $stderr.puts "* Valgrind error spotted:"
+    $stderr.puts err.to_s.split("\n").map{|s| "  #{s}"}
+    $stderr.puts "*"*72
+  end
+
+
+  private
+  def launch_watch_thread(pid, io_r)
+    Thread.start do
+      io_source = REXML::IOSource.new( io_r )
+      listener = ErrorListener.new( self )
+      REXML::Document.parse_stream( io_source, listener )
+    end
+  end
+
+
+end # class ValgrindExecutor
+
+
 # Noddy test class to exercise FlexNBD from the outside for testing.
 #
 class FlexNBD
   attr_reader :bin, :ctrl, :pid, :ip, :port
 
+  class << self
+    def counter
+      Dir['tmp/*'].select{|f| File.file?(f)}.length + 1
+    end
+  end
+
   def initialize(bin, ip, port)
     @bin  = bin
     @debug = `#{@bin} serve --help` =~ /--verbose/ ? "--verbose" : ""
-    @valgrind = ENV['VALGRIND'] ? "valgrind " : ""
-    @bin = "#{@valgrind}#{@bin}"
     raise "#{bin} not executable" unless File.executable?(bin)
+    @executor = ENV['VALGRIND'] ? ValgrindExecutor.new : Executor.new
     @ctrl = "/tmp/.flexnbd.ctrl.#{Time.now.to_i}.#{rand}"
     @ip = ip
     @port = port
     @kill = false
   end
 
+
   def debug?
     !@debug.empty?
   end
@@ -30,7 +156,7 @@ class FlexNBD
 
 
   def serve_cmd( file, acl )
-    "#{@bin} serve "\
+    "#{bin} serve "\
       "--addr #{ip} "\
       "--port #{port} "\
       "--file #{file} "\
@@ -41,7 +167,7 @@ class FlexNBD
 
 
   def read_cmd( offset, length )
-    "#{@bin} read "\
+    "#{bin} read "\
       "--addr #{ip} "\
       "--port #{port} "\
       "--from #{offset} "\
@@ -51,7 +177,7 @@ class FlexNBD
 
 
   def write_cmd( offset, data )
-    "#{@bin} write "\
+    "#{bin} write "\
       "--addr #{ip} "\
       "--port #{port} "\
       "--from #{offset} "\
@@ -65,7 +191,7 @@ class FlexNBD
     cmd =serve_cmd( file, acl )
     debug( cmd )
 
-    @pid = fork do exec(cmd) end
+    @pid = @executor.run( cmd )
     start_wait_thread( @pid )
 
     while !File.socket?(ctrl)
@@ -106,7 +232,7 @@ class FlexNBD
   def write(offset, data)
     cmd = write_cmd( offset, data )
     debug( cmd )
-    
+
     IO.popen(cmd, "w") do |fh|
       fh.write(data)
     end