Use an approach to build stanza that do not require a "builder" abstraction

stanza/xmpp_test.go

@@ -10,6 +10,15 @@ import (
 // marshal / unmarshal. There is no need to manage them on the manually
 // crafted structure.
 func xmlEqual(x, y interface{}) bool {
+	return cmp.Equal(x, y, xmlOpts())
+}
+
+// xmlDiff compares xml structures ignoring namespace preferences
+func xmlDiff(x, y interface{}) string {
+	return cmp.Diff(x, y, xmlOpts())
+}
+
+func xmlOpts() cmp.Options {
 	alwaysEqual := cmp.Comparer(func(_, _ interface{}) bool { return true })
 	opts := cmp.Options{
 		cmp.FilterValues(func(x, y interface{}) bool {
@@ -20,10 +29,12 @@ func xmlEqual(x, y interface{}) bool {
 				if xx == zero || yy == zero {
 					return true
 				}
+				if xx.Space == "" || yy.Space == "" {
+					return true
+				}
 			}
 			return false
 		}, alwaysEqual),
 	}
-
-	return cmp.Equal(x, y, opts)
+	return opts
 }