[jingle] Add unit test to check that there are no redundant namespaces

Related to SMACK-917.

smack-extensions/src/test/java/org/jivesoftware/smackx/jingle/element/JingleTest.java

@@ -0,0 +1,48 @@
+/**
+ *
+ * Copyright 2021 Florian Schmaus
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.jivesoftware.smackx.jingle.element;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import org.jivesoftware.smack.packet.StreamOpen;
+
+import org.junit.jupiter.api.Test;
+
+public class JingleTest {
+
+    @Test
+    public void noRedundantNamespaceTest() {
+        Jingle.Builder jingleBuilder = Jingle.builder("test-id");
+        jingleBuilder.setSessionId("MySession");
+        jingleBuilder.setAction(JingleAction.content_accept);
+
+        JingleContent.Builder jingleContentBuilder = JingleContent.getBuilder();
+        jingleContentBuilder.setName("Hello world");
+        jingleContentBuilder.setCreator(JingleContent.Creator.initiator);
+
+        jingleBuilder.addJingleContent(jingleContentBuilder.build());
+        Jingle iq = jingleBuilder.build();
+
+        String actualXml = iq.toXML(StreamOpen.CLIENT_NAMESPACE).toString();
+        String expectedXml
+                        = "<iq id='test-id' type='set'>"
+                        + "<jingle xmlns='urn:xmpp:jingle:1' action='content-accept' sid='MySession'>"
+                        + "<content creator='initiator' name='Hello world'/>"
+                        + "</jingle></iq>";
+        assertEquals(expectedXml, actualXml);
+    }
+}