diff --git a/src/pkg/strings/replace_test.go b/src/pkg/strings/replace_test.go
new file mode 100644
index 0000000..a7677a1
--- /dev/null
+++ b/src/pkg/strings/replace_test.go
@@ -0,0 +1,75 @@
+// 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 strings_test
+
+import (
+	. "strings"
+	"testing"
+)
+
+type ReplacerTest struct {
+	m   *Replacer
+	in  string
+	out string
+}
+
+var htmlEscaper = NewReplacer("&", "&amp;", "<", "&lt;", ">", "&gt;", "\"", "&quot;")
+
+// The http package's old HTML escaping function.
+func oldhtmlEscape(s string) string {
+	s = Replace(s, "&", "&amp;", -1)
+	s = Replace(s, "<", "&lt;", -1)
+	s = Replace(s, ">", "&gt;", -1)
+	s = Replace(s, "\"", "&quot;", -1)
+	s = Replace(s, "'", "&apos;", -1)
+	return s
+}
+
+var replacer = NewReplacer("aaa", "3[aaa]", "aa", "2[aa]", "a", "1[a]", "i", "i",
+	"longerst", "most long", "longer", "medium", "long", "short",
+	"X", "Y", "Y", "Z")
+
+var ReplacerTests = []ReplacerTest{
+	{htmlEscaper, "No changes", "No changes"},
+	{htmlEscaper, "I <3 escaping & stuff", "I &lt;3 escaping &amp; stuff"},
+	{htmlEscaper, "&&&", "&amp;&amp;&amp;"},
+	{replacer, "fooaaabar", "foo3[aaa]b1[a]r"},
+	{replacer, "long, longerst, longer", "short, most long, medium"},
+	{replacer, "XiX", "YiY"},
+}
+
+func TestReplacer(t *testing.T) {
+	for i, tt := range ReplacerTests {
+		if s := tt.m.Replace(tt.in); s != tt.out {
+			t.Errorf("%d. Replace(%q) = %q, want %q", i, tt.in, s, tt.out)
+		}
+	}
+}
+
+var slowReplacer = NewReplacer("&&", "&amp;", "<<", "&lt;", ">>", "&gt;", "\"\"", "&quot;", "''", "&apos;")
+
+func BenchmarkReplacerSingleByte(b *testing.B) {
+	str := "I <3 benchmarking html & other stuff too >:D"
+	n := 0
+	for i := 0; i < b.N; i++ {
+		n += len(htmlEscaper.Replace(str))
+	}
+}
+
+func BenchmarkReplaceMap(b *testing.B) {
+	str := "I <<3 benchmarking html && other stuff too >>:D"
+	n := 0
+	for i := 0; i < b.N; i++ {
+		n += len(slowReplacer.Replace(str))
+	}
+}
+
+func BenchmarkOldHTTPHTMLReplace(b *testing.B) {
+	str := "I <3 benchmarking html & other stuff too >:D"
+	n := 0
+	for i := 0; i < b.N; i++ {
+		n += len(oldhtmlEscape(str))
+	}
+}