diff --git a/ChangeLog b/ChangeLog
index e53fc4746f..825483d0fe 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Sun Jan  3 01:29:18 2010  Tanaka Akira  <akr@fsij.org>
+
+	* lib/resolv.rb (Resolv::DNS::Message::MessageDecoder#inspect):
+	  implemented.
+
 Sat Jan  2 15:57:54 2010  Tanaka Akira  <akr@fsij.org>
 
 	* lib/resolv.rb (Resolv::DNS#initialize): new option :nameserver_port.
diff --git a/lib/resolv.rb b/lib/resolv.rb
index 560f1dfe95..4ac24f3b36 100644
--- a/lib/resolv.rb
+++ b/lib/resolv.rb
@@ -1385,6 +1385,10 @@ class Resolv
           yield self
         end
 
+        def inspect
+          "\#<#{self.class}: #{@data[0, @index].inspect} #{@data[@index..-1].inspect}>"
+        end
+
         def get_length16
           len, = self.get_unpack('n')
           save_limit = @limit
@@ -2097,8 +2101,11 @@ class Resolv
     end
 
     def initialize(address) # :nodoc:
-      unless address.kind_of?(String) && address.length == 4
-        raise ArgumentError.new('IPv4 address must be 4 bytes')
+      unless address.kind_of?(String)
+        raise ArgumentError, 'IPv4 address must be a string'
+      end
+      unless address.length == 4
+        raise ArgumentError, "IPv4 address expects 4 bytes but #{address.length} bytes"
       end
       @address = address
     end
diff --git a/test/resolv/test_dns.rb b/test/resolv/test_dns.rb
new file mode 100644
index 0000000000..0ab59665a3
--- /dev/null
+++ b/test/resolv/test_dns.rb
@@ -0,0 +1,107 @@
+require 'test/unit'
+require 'resolv'
+require 'socket'
+
+class TestResolvDNS < Test::Unit::TestCase
+  def setup
+    @save_do_not_reverse_lookup = BasicSocket.do_not_reverse_lookup
+    BasicSocket.do_not_reverse_lookup = true
+  end
+
+  def teardown
+    BasicSocket.do_not_reverse_lookup = @save_do_not_reverse_lookup
+  end
+
+  def with_udp(host, port)
+    u = UDPSocket.new
+    begin
+      u.bind(host, port)
+      yield u
+    ensure
+      u.close
+    end
+  end
+
+  def test_query_ipv4_address
+    with_udp('127.0.0.1', 0) {|u|
+      _, server_port, _, server_address = u.addr
+      begin
+        th = Thread.new {
+          Resolv::DNS.open(:nameserver_port => [[server_address, server_port]]) {|dns|
+            dns.getresources("foo.example.org", Resolv::DNS::Resource::IN::A)
+          }
+        }
+        msg, (af, client_port, _, client_address) = u.recvfrom(4096)
+        id, word2, qdcount, ancount, nscount, arcount = msg.unpack("nnnnnn")
+        qr =     (word2 & 0x8000) >> 15
+        opcode = (word2 & 0x7800) >> 11
+        aa =     (word2 & 0x0400) >> 10
+        tc =     (word2 & 0x0200) >> 9
+        rd =     (word2 & 0x0100) >> 8
+        ra =     (word2 & 0x0080) >> 7
+        z =      (word2 & 0x0070) >> 4
+        rcode =   word2 & 0x000f
+        rest = msg[12..-1]
+        assert_equal(0, qr) # 0:query 1:response
+        assert_equal(0, opcode) # 0:QUERY 1:IQUERY 2:STATUS
+        assert_equal(0, aa) # Authoritative Answer
+        assert_equal(0, tc) # TrunCation
+        assert_equal(1, rd) # Recursion Desired
+        assert_equal(0, ra) # Recursion Available
+        assert_equal(0, z) # Reserved for future use
+        assert_equal(0, rcode) # 0:No-error 1:Format-error 2:Server-failure 3:Name-Error 4:Not-Implemented 5:Refused
+        assert_equal(1, qdcount) # number of entries in the question section.
+        assert_equal(0, ancount) # number of entries in the answer section.
+        assert_equal(0, nscount) # number of entries in the authority records section.
+        assert_equal(0, arcount) # number of entries in the additional records section.
+        name = [3, "foo", 7, "example", 3, "org", 0].pack("Ca*Ca*Ca*C")
+        assert_operator(rest, :start_with?, name)
+        rest = rest[name.length..-1]
+        assert_equal(4, rest.length)
+        qtype, qclass = rest.unpack("nn")
+        assert_equal(1, qtype) # A
+        assert_equal(1, qtype) # IN
+        id = id
+        qr = 1
+        opcode = opcode
+        aa = 0
+        tc = 0
+        rd = rd
+        ra = 1
+        z = 0
+        rcode = 0
+        qdcount = 0
+        ancount = 1
+        nscount = 0
+        arcount = 0
+        word2 = (qr << 15) |
+                (opcode << 11) |
+                (aa << 10) |
+                (tc << 9) |
+                (rd << 8) |
+                (ra << 7) |
+                (z << 4) |
+                rcode
+        msg = [id, word2, qdcount, ancount, nscount, arcount].pack("nnnnnn")
+        type = 1
+        klass = 1
+        ttl = 3600
+        rdlength = 4
+        rdata = [192,0,2,1].pack("CCCC") # 192.0.2.1 (TEST-NET address) RFC 3330
+        rr = [name, type, klass, ttl, rdlength, rdata].pack("a*nnNna*")
+        msg << rr
+        u.send(msg, 0, client_address, client_port)
+        result = th.value
+        assert_instance_of(Array, result)
+        assert_equal(1, result.length)
+        rr = result[0]
+        assert_instance_of(Resolv::DNS::Resource::IN::A, rr)
+        assert_instance_of(Resolv::IPv4, rr.address)
+        assert_equal("192.0.2.1", rr.address.to_s)
+        assert_equal(3600, rr.ttl)
+      ensure
+        th.join
+      end
+    }
+  end
+end