plumbing/packfile: test UpdateObjectStorage empty packfile error

Signed-off-by: Javi Fontan <jfontan@gmail.com>

Author: jfontan

plumbing/format/packfile/common_test.go

@@ -1,15 +1,29 @@
 package packfile
 
 import (
+	"bytes"
 	"testing"
 
 	"gopkg.in/src-d/go-git.v4/plumbing"
+	"gopkg.in/src-d/go-git.v4/storage/memory"
 
 	. "gopkg.in/check.v1"
 )
 
 func Test(t *testing.T) { TestingT(t) }
 
+type CommonSuite struct{}
+
+var _ = Suite(&CommonSuite{})
+
+func (s *CommonSuite) TestEmptyUpdateObjectStorage(c *C) {
+	var buf bytes.Buffer
+	sto := memory.NewStorage()
+
+	err := UpdateObjectStorage(sto, &buf)
+	c.Assert(err, Equals, ErrEmptyPackfile)
+}
+
 func newObject(t plumbing.ObjectType, cont []byte) plumbing.EncodedObject {
 	o := plumbing.MemoryObject{}
 	o.SetType(t)