diff --git a/envelop/envelop_test.go b/envelop/envelop_test.go
index 9d2fea4..c7100df 100644
--- a/envelop/envelop_test.go
+++ b/envelop/envelop_test.go
@@ -4,10 +4,11 @@ import (
 	"archive/zip"
 	"bytes"
 	"errors"
-	"github.com/didiercrunch/filou/helper"
 	"io"
 	"reflect"
 	"testing"
+
+	"github.com/didiercrunch/filou/helper"
 )
 
 type mockPayload struct {
diff --git a/integration/doc.go b/integration/doc.go
new file mode 100644
index 0000000..b08b412
--- /dev/null
+++ b/integration/doc.go
@@ -0,0 +1,5 @@
+package integration
+
+/*
+Integration tests.
+*/
diff --git a/integration/enveloppayload_test.go b/integration/enveloppayload_test.go
index 240dd4b..2bc206e 100644
--- a/integration/enveloppayload_test.go
+++ b/integration/enveloppayload_test.go
@@ -1,10 +1,12 @@
 package integration
 
 import (
+	"archive/zip"
 	"bytes"
 	"testing"
 
 	"github.com/didiercrunch/filou/envelop"
+	"github.com/didiercrunch/filou/helper"
 	"github.com/didiercrunch/filou/payload"
 )
 
@@ -33,7 +35,16 @@ func (this *mockSigner) Sign(data []byte) ([]byte, error) {
 func TestPayloadCanBeUseInEnvelop(t *testing.T) {
 	payload_ := payload.GetDefaultPayload(bytes.NewBufferString("some data to encrypt"))
 	envelop := envelop.NewEnveloper(&mockEncryptor{}, payload_, &mockSigner{})
-	if envelop == nil {
-		t.Fail()
+	w := helper.NewMockIoWriter()
+	if err := envelop.WriteToWriter(w); err != nil {
+		t.Error(err)
+	}
+	r, err := zip.NewReader(w.ReaderAt(), int64(w.Length()))
+	if err != nil {
+		t.Error(err)
+		return
+	}
+	if len(r.File) != 3 {
+		t.Error("wrong file number")
 	}
 }
diff --git a/payload/payload_test.go b/payload/payload_test.go
index 335c5c3..1452e0b 100644
--- a/payload/payload_test.go
+++ b/payload/payload_test.go
@@ -4,10 +4,11 @@ import (
 	"bytes"
 	"errors"
 	"fmt"
-	"github.com/didiercrunch/filou/helper"
 	"io/ioutil"
 	"reflect"
 	"testing"
+
+	"github.com/didiercrunch/filou/helper"
 )
 
 func TestPayloadGetHashMethod(t *testing.T) {