Adding test at byte level

pkg/storage/donut/data/data_v1/data.go

@@ -82,10 +82,9 @@ func WriteData(target io.Writer, header DataHeader, data io.Reader) error {
 	// encode header
 	encoder := gob.NewEncoder(&headerBuffer)
 	encoder.Encode(header)
-	// write length of header
-	if err := binary.Write(target, binary.LittleEndian, int64(headerBuffer.Len())); err != nil {
-		return err
-	}
+
+	// write version
+	binary.Write(target, binary.LittleEndian, uint32(1))
 
 	// write encoded header
 	if _, err := io.Copy(target, &headerBuffer); err != nil {

pkg/storage/donut/data/data_v1/data_test.go

@@ -18,6 +18,9 @@ package data_v1
 
 import (
 	"bytes"
+	"encoding/binary"
+	"encoding/gob"
+	"io"
 	"testing"
 
 	. "gopkg.in/check.v1"
@@ -46,4 +49,23 @@ func (s *MySuite) TestSingleWrite(c *C) {
 
 	err := WriteData(&testBuffer, header, bytes.NewBufferString(testData))
 	c.Assert(err, IsNil)
+
+	actualVersion := make([]byte, 4)
+	_, err = testBuffer.Read(actualVersion)
+	c.Assert(err, IsNil)
+	c.Assert(binary.LittleEndian.Uint32(actualVersion), DeepEquals, uint32(1))
+
+	actualHeader := DataHeader{}
+
+	decoder := gob.NewDecoder(&testBuffer)
+	decoder.Decode(&actualHeader)
+
+	c.Assert(actualHeader, DeepEquals, header)
+
+	var actualData bytes.Buffer
+
+	dataLength, err := io.Copy(&actualData, &testBuffer)
+	c.Assert(dataLength, Equals, int64(len(testData)))
+	c.Assert(actualData.Bytes(), DeepEquals, []byte(testData))
+	c.Assert(err, IsNil)
 }