Add test for serialization interaction

ext/dom/tests/modern/common/namespace_sxe_interaction.phpt

@@ -0,0 +1,53 @@
+--TEST--
+Serialization interaction between simplexml and dom for namespaces
+--EXTENSIONS--
+dom
+simplexml
+--FILE--
+<?php
+
+$dom = Dom\XMLDocument::createFromString('<root/>');
+$sxe = simplexml_import_dom($dom);
+
+$sxe->addAttribute('a:attr', 'value', 'urn:a');
+$sxe->addChild('b:child', 'value', 'urn:b');
+$sxe->addChild('foo', 'value2');
+$dom->documentElement->firstElementChild->appendChild($dom->createElementNS('urn:c', 'c:child'));
+
+echo "namespace c: ";
+var_dump($dom->documentElement->firstElementChild->firstElementChild->lookupNamespaceURI('c'));
+echo "namespace b: ";
+var_dump($dom->documentElement->firstElementChild->firstElementChild->lookupNamespaceURI('b'));
+echo "namespace a: ";
+var_dump($dom->documentElement->firstElementChild->firstElementChild->lookupNamespaceURI('a'));
+
+echo "=== serialize SimpleXML ===\n";
+
+echo $sxe->saveXML(), "\n";
+
+echo "=== serialize DOM ===\n";
+
+echo $dom->saveXML(), "\n\n";
+
+echo "=== serialize imported DOM ===\n";
+
+// Importing should yield the exact same document
+$new_dom = Dom\XMLDocument::createEmpty();
+$new_dom->append($new_dom->importNode($dom->documentElement, true));
+echo $new_dom->saveXML(), "\n";
+
+?>
+--EXPECT--
+namespace c: string(5) "urn:c"
+namespace b: string(5) "urn:b"
+namespace a: NULL
+=== serialize SimpleXML ===
+<?xml version="1.0" encoding="UTF-8"?>
+<root xmlns:a="urn:a" a:attr="value"><b:child xmlns:b="urn:b">value<c:child xmlns:c="urn:c"/></b:child></root>
+=== serialize DOM ===
+<?xml version="1.0" encoding="UTF-8"?>
+<root xmlns:a="urn:a" a:attr="value"><b:child xmlns:b="urn:b">value<c:child xmlns:c="urn:c"/></b:child></root>
+
+=== serialize imported DOM ===
+<?xml version="1.0" encoding="UTF-8"?>
+<root xmlns:a="urn:a" a:attr="value"><b:child xmlns:b="urn:b">value<c:child xmlns:c="urn:c"/></b:child></root>