added tests

updated go version and packages

generator/format_test.go

@@ -0,0 +1,45 @@
+package generator
+
+import "testing"
+
+func TestGenerator_StringToFormat(t *testing.T) {
+	g, err := NewGenerator(Config{})
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	formats := []string{"jpg", "jpeg", "png", "gif", "bmp", "webp", "ico", ""}
+
+	for _, format := range formats {
+		format, err := g.StringToFormat(format)
+		if err != nil {
+			t.Error(err)
+		}
+
+		if !isFormat(format) {
+			t.Error("format not match")
+		}
+	}
+}
+
+func TestGenerator_StringToFormatError(t *testing.T) {
+	g, err := NewGenerator(Config{})
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	_, err = g.StringToFormat("notaformat")
+	if err == nil {
+		t.Error("format did not return error")
+	}
+}
+
+func isFormat(t interface{}) bool {
+	switch t.(type) {
+	case Format:
+		return true
+	default:
+		return false
+
+	}
+}