diff --git a/src/lib/io/bytebuffer_test.go b/src/lib/io/bytebuffer_test.go
new file mode 100644
index 0000000..6a4f3c9
--- /dev/null
+++ b/src/lib/io/bytebuffer_test.go
@@ -0,0 +1,146 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package io
+
+import (
+	"io";
+	"rand";
+	"testing";
+)
+
+
+const N = 10000;  // make this bigger for a larger (and slower) test
+var data []byte;  // test data for write tests
+
+
+func init() {
+	data = make([]byte, N);
+	for i := 0; i < len(data); i++ {
+		data[i] = 'a' + byte(i % 26)
+	}
+}
+
+
+// Verify that contents of buf match the string s.
+func check(t *testing.T, testname string, buf *ByteBuffer, s string) {
+	if buf.Len() != len(buf.Data()) {
+		t.Errorf("%s: buf.Len() == %d, len(buf.Data()) == %d\n", testname, buf.Len(), len(buf.Data()))
+	}
+
+	if buf.Len() != len(s) {
+		t.Errorf("%s: buf.Len() == %d, len(s) == %d\n", testname, buf.Len(), len(s))
+	}
+
+	if string(buf.Data()) != s {
+		t.Errorf("%s: string(buf.Data()) == %q, s == %q\n", testname, string(buf.Data()), s)
+	}
+}
+
+
+// Fill buf through n writes of fub.
+// The initial contents of buf corresponds to the string s;
+// the result is the final contents of buf returned as a string.
+func fill(t *testing.T, testname string, buf *ByteBuffer, s string, n int, fub []byte) string {
+	check(t, testname + " (fill 1)", buf, s);
+	for ; n > 0; n-- {
+		m, err := buf.Write(fub);
+		if m != len(fub) {
+			t.Errorf(testname + " (fill 2): m == %d, expected %d\n", m, len(fub));
+		}
+		if err != nil {
+			t.Errorf(testname + " (fill 3): err should always be nil, found err == %s\n", err);
+		}
+		s += string(fub);
+		check(t, testname + " (fill 4)", buf, s);
+	}
+	return s;
+}
+
+
+// Empty buf through repeated reads into fub.
+// The initial contents of buf corresponds to the string s.
+func empty(t *testing.T, testname string, buf *ByteBuffer, s string, fub []byte) {
+	check(t, testname + " (empty 1)", buf, s);
+
+	for {
+		n, err := buf.Read(fub);
+		if n == 0 {
+			break;
+		}
+		if err != nil {
+			t.Errorf(testname + " (empty 2): err should always be nil, found err == %s\n", err);
+		}
+		s = s[n : len(s)];
+		check(t, testname + " (empty 3)", buf, s);
+	}
+
+	check(t, testname + " (empty 4)", buf, "");
+}
+
+
+func TestBasicOperations(t *testing.T) {
+	var buf ByteBuffer;
+
+	for i := 0; i < 5; i++ {
+		check(t, "TestBasicOperations (1)", &buf, "");
+
+		buf.Reset();
+		check(t, "TestBasicOperations (2)", &buf, "");
+
+		n, err := buf.Write(data[0 : 1]);
+		if n != 1 {
+			t.Errorf("wrote 1 byte, but n == %d\n", n);
+		}
+		if err != nil {
+			t.Errorf("err should always be nil, but err == %s\n", err);
+		}
+		check(t, "TestBasicOperations (3)", &buf, "a");
+
+		n, err = buf.Write(data[1 : 26]);
+		if n != 25 {
+			t.Errorf("wrote 25 bytes, but n == %d\n", n);
+		}
+		check(t, "TestBasicOperations (4)", &buf, string(data[0 : 26]));
+
+		empty(t, "TestBasicOperations (5)", &buf, string(data[0 : 26]), make([]byte, 5));
+		empty(t, "TestBasicOperations (6)", &buf, "", make([]byte, 100));
+	}
+}
+
+
+func TestLargeWrites(t *testing.T) {
+	var buf ByteBuffer;
+	for i := 3; i < 30; i += 3 {
+		s := fill(t, "TestLargeWrites (1)", &buf, "", 5, data);
+		empty(t, "TestLargeWrites (2)", &buf, s, make([]byte, len(data)/i));
+	}
+	check(t, "TestLargeWrites (3)", &buf, "");
+}
+
+
+func TestLargeReads(t *testing.T) {
+	var buf ByteBuffer;
+	for i := 3; i < 30; i += 3 {
+		s := fill(t, "TestLargeReads (1)", &buf, "", 5, data[0 : len(data)/i]);
+		empty(t, "TestLargeReads (2)", &buf, s, make([]byte, len(data)));
+	}
+	check(t, "TestLargeReads (3)", &buf, "");
+}
+
+
+func TestMixedReadsAndWrites(t *testing.T) {
+	var buf ByteBuffer;
+	s := "";
+	for i := 0; i < 50; i++ {
+		wlen := rand.Intn(len(data));
+		s = fill(t, "TestMixedReadsAndWrites (1)", &buf, s, 1, data[0 : wlen]);
+
+		rlen := rand.Intn(len(data));
+		fub := make([]byte, rlen);
+		n, err := buf.Read(fub);
+		s = s[n : len(s)];
+	}
+	empty(t, "TestMixedReadsAndWrites (2)", &buf, s, make([]byte, buf.Len()));
+}