diff --git a/commonmark_test.go b/commonmark_test.go
index 64d5e3d..4e15daa 100644
--- a/commonmark_test.go
+++ b/commonmark_test.go
@@ -1,10 +1,12 @@
-package goldmark
+package goldmark_test
 
 import (
 	"encoding/json"
 	"io/ioutil"
 	"testing"
 
+	. "github.com/yuin/goldmark"
+	"github.com/yuin/goldmark/testutil"
 	"github.com/yuin/goldmark/renderer/html"
 )
 
@@ -26,9 +28,9 @@ func TestSpec(t *testing.T) {
 	if err := json.Unmarshal(bs, &testCases); err != nil {
 		panic(err)
 	}
-	cases := []MarkdownTestCase{}
+	cases := []testutil.MarkdownTestCase{}
 	for _, c := range testCases {
-		cases = append(cases, MarkdownTestCase{
+		cases = append(cases, testutil.MarkdownTestCase{
 			No:       c.Example,
 			Markdown: c.Markdown,
 			Expected: c.HTML,
@@ -38,5 +40,5 @@ func TestSpec(t *testing.T) {
 		html.WithXHTML(),
 		html.WithUnsafe(),
 	))
-	DoTestCases(markdown, cases, t)
+	testutil.DoTestCases(markdown, cases, t)
 }
diff --git a/extension/definition_list_test.go b/extension/definition_list_test.go
index 1cbf167..2ee3c61 100644
--- a/extension/definition_list_test.go
+++ b/extension/definition_list_test.go
@@ -1,9 +1,11 @@
 package extension
 
 import (
-	"github.com/yuin/goldmark"
-	"github.com/yuin/goldmark/renderer/html"
 	"testing"
+
+	"github.com/yuin/goldmark"
+	"github.com/yuin/goldmark/testutil"
+	"github.com/yuin/goldmark/renderer/html"
 )
 
 func TestDefinitionList(t *testing.T) {
@@ -15,5 +17,5 @@ func TestDefinitionList(t *testing.T) {
 			DefinitionList,
 		),
 	)
-	goldmark.DoTestCaseFile(markdown, "_test/definition_list.txt", t)
+	testutil.DoTestCaseFile(markdown, "_test/definition_list.txt", t)
 }
diff --git a/extension/footnote_test.go b/extension/footnote_test.go
index b5ce90c..0f2e0b5 100644
--- a/extension/footnote_test.go
+++ b/extension/footnote_test.go
@@ -1,9 +1,11 @@
 package extension
 
 import (
-	"github.com/yuin/goldmark"
-	"github.com/yuin/goldmark/renderer/html"
 	"testing"
+
+	"github.com/yuin/goldmark"
+	"github.com/yuin/goldmark/testutil"
+	"github.com/yuin/goldmark/renderer/html"
 )
 
 func TestFootnote(t *testing.T) {
@@ -15,5 +17,5 @@ func TestFootnote(t *testing.T) {
 			Footnote,
 		),
 	)
-	goldmark.DoTestCaseFile(markdown, "_test/footnote.txt", t)
+	testutil.DoTestCaseFile(markdown, "_test/footnote.txt", t)
 }
diff --git a/extension/linkify_test.go b/extension/linkify_test.go
index 5a80b95..040d1ab 100644
--- a/extension/linkify_test.go
+++ b/extension/linkify_test.go
@@ -1,9 +1,11 @@
 package extension
 
 import (
-	"github.com/yuin/goldmark"
-	"github.com/yuin/goldmark/renderer/html"
 	"testing"
+
+	"github.com/yuin/goldmark"
+	"github.com/yuin/goldmark/testutil"
+	"github.com/yuin/goldmark/renderer/html"
 )
 
 func TestLinkify(t *testing.T) {
@@ -15,5 +17,5 @@ func TestLinkify(t *testing.T) {
 			Linkify,
 		),
 	)
-	goldmark.DoTestCaseFile(markdown, "_test/linkify.txt", t)
+	testutil.DoTestCaseFile(markdown, "_test/linkify.txt", t)
 }
diff --git a/extension/strikethrough_test.go b/extension/strikethrough_test.go
index 891409e..05660ee 100644
--- a/extension/strikethrough_test.go
+++ b/extension/strikethrough_test.go
@@ -1,9 +1,11 @@
 package extension
 
 import (
-	"github.com/yuin/goldmark"
-	"github.com/yuin/goldmark/renderer/html"
 	"testing"
+
+	"github.com/yuin/goldmark"
+	"github.com/yuin/goldmark/testutil"
+	"github.com/yuin/goldmark/renderer/html"
 )
 
 func TestStrikethrough(t *testing.T) {
@@ -15,5 +17,5 @@ func TestStrikethrough(t *testing.T) {
 			Strikethrough,
 		),
 	)
-	goldmark.DoTestCaseFile(markdown, "_test/strikethrough.txt", t)
+	testutil.DoTestCaseFile(markdown, "_test/strikethrough.txt", t)
 }
diff --git a/extension/table_test.go b/extension/table_test.go
index 7e38896..655f3fc 100644
--- a/extension/table_test.go
+++ b/extension/table_test.go
@@ -1,9 +1,11 @@
 package extension
 
 import (
-	"github.com/yuin/goldmark"
-	"github.com/yuin/goldmark/renderer/html"
 	"testing"
+
+	"github.com/yuin/goldmark"
+	"github.com/yuin/goldmark/testutil"
+	"github.com/yuin/goldmark/renderer/html"
 )
 
 func TestTable(t *testing.T) {
@@ -15,5 +17,5 @@ func TestTable(t *testing.T) {
 			Table,
 		),
 	)
-	goldmark.DoTestCaseFile(markdown, "_test/table.txt", t)
+	testutil.DoTestCaseFile(markdown, "_test/table.txt", t)
 }
diff --git a/extension/tasklist_test.go b/extension/tasklist_test.go
index 6fc74d5..594471f 100644
--- a/extension/tasklist_test.go
+++ b/extension/tasklist_test.go
@@ -1,9 +1,11 @@
 package extension
 
 import (
-	"github.com/yuin/goldmark"
-	"github.com/yuin/goldmark/renderer/html"
 	"testing"
+
+	"github.com/yuin/goldmark"
+	"github.com/yuin/goldmark/testutil"
+	"github.com/yuin/goldmark/renderer/html"
 )
 
 func TestTaskList(t *testing.T) {
@@ -15,5 +17,5 @@ func TestTaskList(t *testing.T) {
 			TaskList,
 		),
 	)
-	goldmark.DoTestCaseFile(markdown, "_test/tasklist.txt", t)
+	testutil.DoTestCaseFile(markdown, "_test/tasklist.txt", t)
 }
diff --git a/extension/typographer_test.go b/extension/typographer_test.go
index 6646314..bc1b21f 100644
--- a/extension/typographer_test.go
+++ b/extension/typographer_test.go
@@ -1,9 +1,11 @@
 package extension
 
 import (
-	"github.com/yuin/goldmark"
-	"github.com/yuin/goldmark/renderer/html"
 	"testing"
+
+	"github.com/yuin/goldmark"
+	"github.com/yuin/goldmark/testutil"
+	"github.com/yuin/goldmark/renderer/html"
 )
 
 func TestTypographer(t *testing.T) {
@@ -15,5 +17,5 @@ func TestTypographer(t *testing.T) {
 			Typographer,
 		),
 	)
-	goldmark.DoTestCaseFile(markdown, "_test/typographer.txt", t)
+	testutil.DoTestCaseFile(markdown, "_test/typographer.txt", t)
 }
diff --git a/extra_test.go b/extra_test.go
index e2548b2..23d3506 100644
--- a/extra_test.go
+++ b/extra_test.go
@@ -1,8 +1,10 @@
-package goldmark
+package goldmark_test
 
 import (
 	"testing"
 
+	. "github.com/yuin/goldmark"
+	"github.com/yuin/goldmark/testutil"
 	"github.com/yuin/goldmark/renderer/html"
 )
 
@@ -11,5 +13,5 @@ func TestDefinitionList(t *testing.T) {
 		html.WithXHTML(),
 		html.WithUnsafe(),
 	))
-	DoTestCaseFile(markdown, "_test/extra.txt", t)
+	testutil.DoTestCaseFile(markdown, "_test/extra.txt", t)
 }
diff --git a/options_test.go b/options_test.go
index 2018bd1..d024a52 100644
--- a/options_test.go
+++ b/options_test.go
@@ -1,8 +1,11 @@
-package goldmark
+package goldmark_test
 
 import (
-	"github.com/yuin/goldmark/parser"
 	"testing"
+
+	. "github.com/yuin/goldmark"
+	"github.com/yuin/goldmark/testutil"
+	"github.com/yuin/goldmark/parser"
 )
 
 func TestAttributeAndAutoHeadingID(t *testing.T) {
@@ -12,5 +15,5 @@ func TestAttributeAndAutoHeadingID(t *testing.T) {
 			parser.WithAutoHeadingID(),
 		),
 	)
-	DoTestCaseFile(markdown, "_test/options.txt", t)
+	testutil.DoTestCaseFile(markdown, "_test/options.txt", t)
 }
diff --git a/testutil.go b/testutil/testutil.go
similarity index 90%
rename from testutil.go
rename to testutil/testutil.go
index 9f3ba52..4a83a03 100644
--- a/testutil.go
+++ b/testutil/testutil.go
@@ -1,4 +1,4 @@
-package goldmark
+package testutil
 
 import (
 	"bufio"
@@ -9,6 +9,7 @@ import (
 	"strconv"
 	"strings"
 
+	"github.com/yuin/goldmark"
 	"github.com/yuin/goldmark/util"
 )
 
@@ -29,7 +30,7 @@ type MarkdownTestCase struct {
 const attributeSeparator = "//- - - - - - - - -//"
 const caseSeparator = "//= = = = = = = = = = = = = = = = = = = = = = = =//"
 
-func DoTestCaseFile(m Markdown, filename string, t TestingT) {
+func DoTestCaseFile(m goldmark.Markdown, filename string, t TestingT) {
 	fp, err := os.Open(filename)
 	if err != nil {
 		panic(err)
@@ -85,13 +86,13 @@ func DoTestCaseFile(m Markdown, filename string, t TestingT) {
 	DoTestCases(m, cases, t)
 }
 
-func DoTestCases(m Markdown, cases []MarkdownTestCase, t TestingT) {
+func DoTestCases(m goldmark.Markdown, cases []MarkdownTestCase, t TestingT) {
 	for _, testCase := range cases {
 		DoTestCase(m, testCase, t)
 	}
 }
 
-func DoTestCase(m Markdown, testCase MarkdownTestCase, t TestingT) {
+func DoTestCase(m goldmark.Markdown, testCase MarkdownTestCase, t TestingT) {
 	var ok bool
 	var out bytes.Buffer
 	defer func() {
diff --git a/testutil_test.go b/testutil/testutil_test.go
similarity index 90%
rename from testutil_test.go
rename to testutil/testutil_test.go
index 2ab24a6..2000a00 100644
--- a/testutil_test.go
+++ b/testutil/testutil_test.go
@@ -1,4 +1,4 @@
-package goldmark
+package testutil
 
 import "testing"