small refactorings of test code and some methods

thumbnails/pkg/thumbnail/encoding.go

@@ -60,9 +60,7 @@ func EncoderForType(fileType string) Encoder {
 	switch strings.ToLower(fileType) {
 	case "png":
 		return PngEncoder{}
-	case "jpg":
-		fallthrough
-	case "jpeg":
+	case "jpg", "jpeg":
 		return JpegEncoder{}
 	default:
 		return nil

thumbnails/pkg/thumbnail/encoding_test.go

@@ -0,0 +1,22 @@
+package thumbnail
+
+import "testing"
+
+func TestEncoderForType(t *testing.T) {
+	table := map[string]Encoder{
+		"jpg":     JpegEncoder{},
+		"JPG":     JpegEncoder{},
+		"jpeg":    JpegEncoder{},
+		"JPEG":    JpegEncoder{},
+		"png":     PngEncoder{},
+		"PNG":     PngEncoder{},
+		"invalid": nil,
+	}
+
+	for k, v := range table {
+		e := EncoderForType(k)
+		if e != v {
+			t.Fail()
+		}
+	}
+}