added serialization unit tests

AUTHORS

@@ -1,2 +1,3 @@
 ---AUTHORS---
 [Dong-hee Na](https://github.com/corona10/) donghee.na92@gmail.com
+[Gustavo Brunoro](https://github.com/brunoro/) git@hitnail.net

imagehash.go

@@ -70,13 +70,13 @@ func (h *ImageHash) Set(idx int) {
 	h.hash |= 1 << uint(idx)
 }
 
-const strFmt = "%v:%0x"
+const strFmt = "%1s:%016x"
 
-// FromString returns an image hash from a hex representation
+// ImageHashFromString returns an image hash from a hex representation
-func FromString(s string) (*ImageHash, error) {
+func ImageHashFromString(s string) (*ImageHash, error) {
 	var kindStr string
 	var hash uint64
-	_, err := fmt.Sscanf(s, strFmt, kindStr, hash)
+	_, err := fmt.Sscanf(s, strFmt, &kindStr, &hash)
 	if err != nil {
 		return nil, errors.New("Couldn't parse string " + s)
 	}

imagehash_test.go

@@ -6,6 +6,11 @@ package goimagehash
 
 import (
 	"errors"
+	"image"
+	_ "image/jpeg"
+	"os"
+	"reflect"
+	"runtime"
 	"testing"
 )
 
@@ -41,11 +46,58 @@ func TestNewImageHash(t *testing.T) {
 
 		dis, err := hash1.Distance(hash2)
 		if dis != tt.distance {
-			t.Errorf("Distance between %v and %v expected as %d but got %d.", data1, data2, tt.distance, dis)
+			t.Errorf("Distance between %v and %v expected as %d but got %d", data1, data2, tt.distance, dis)
 		}
 		if err != nil && err.Error() != tt.err.Error() {
-			t.Errorf("Expected err %s, actual %s.", tt.err, err)
+			t.Errorf("Expected err %s, actual %s", tt.err, err)
+		}
 	}
 }
 
+func TestSerialization(t *testing.T) {
+	checkErr := func(err error) {
+		if err != nil {
+			t.Errorf("%v", err)
+		}
+	}
+
+	methods := []func(img image.Image) (*ImageHash, error){
+		AverageHash, PerceptionHash, DifferenceHash,
+	}
+	examples := []string{
+		"_examples/sample1.jpg", "_examples/sample2.jpg", "_examples/sample3.jpg", "_examples/sample4.jpg",
+	}
+
+	for _, ex := range examples {
+		file, err := os.Open(ex)
+		checkErr(err)
+
+		defer file.Close()
+
+		img, _, err := image.Decode(file)
+		checkErr(err)
+
+		for _, method := range methods {
+			methodStr := runtime.FuncForPC(reflect.ValueOf(method).Pointer()).Name()
+
+			hash, err := method(img)
+			checkErr(err)
+
+			hex := hash.ToString()
+			// len(kind) == 1, len(":") == 1, len(hash) == 16
+			if len(hex) != 18 {
+				t.Errorf("Got invalid hex string '%v'; %v of '%v'", hex, methodStr, ex)
+			}
+
+			reHash, err := ImageHashFromString(hex)
+			checkErr(err)
+
+			distance, err := hash.Distance(reHash)
+			checkErr(err)
+
+			if distance != 0 {
+				t.Errorf("Original and unserialized objects should be identical, got distance=%v; %v of '%v'", distance, methodStr, ex)
+			}
+		}
+	}
 }