diff --git a/testutil/encoding_test.go b/testutil/encoding_test.go
new file mode 100644
index 0000000000..d07ef1b6b4
--- /dev/null
+++ b/testutil/encoding_test.go
@@ -0,0 +1,33 @@
+package testutil_test
+
+import (
+	"encoding/json"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+
+	"github.com/Finschia/finschia-sdk/testutil"
+)
+
+func TestMustJSONMarshal(t *testing.T) {
+	type tc struct {
+		Name  string `json:"myName"`
+		Order string `json:"myOrder"`
+	}
+
+	a := tc{
+		Name:  "test",
+		Order: "first",
+	}
+	b := new(tc)
+
+	marshaled := testutil.MustJSONMarshal(a)
+	err := json.Unmarshal(marshaled, b)
+	require.NoError(t, err)
+	require.Equal(t, a, *b)
+	require.Panics(t, func() { testutil.MustJSONMarshal(make(chan int)) })
+}
+
+func TestW(t *testing.T) {
+	require.Equal(t, []byte(`"test"`), testutil.W("test"))
+}