Add Sip constructor that takes a URI

Add a constructor to the Sip Noun with a text element URI. Previously,
the only way to do this was to append a Uri Noun to the Sip Noun. Also,
add a couple of unit tests.

Author: juggernaut

src/main/java/com/twilio/sdk/verbs/Sip.java

@@ -8,12 +8,19 @@ public class Sip extends Verb {
     /**
      * Instantiates a new Sip.
      */
-    public Sip() {
-        super(V_SIP, null);
+    public Sip(final String uri) {
+        super(V_SIP, uri);
         this.allowedVerbs = new ArrayList<String>();
         this.allowedVerbs.add(Verb.V_URI);
     }
 
+    /**
+     * Instantiates a new Sip Noun with no URI.
+     */
+    public Sip() {
+        this(null);
+    }
+
     public void setUsername(String username) {
         this.set("username", username);
     }

src/test/java/com/twilio/sdk/verbs/SipTest.java

@@ -0,0 +1,32 @@
+package com.twilio.sdk.verbs;
+
+import org.junit.Test;
+
+import static org.junit.Assert.assertEquals;
+
+public class SipTest {
+
+    /**
+     * Test the SIP noun with a text element representing the URI.
+     */
+    @Test
+    public void testBasicSip() {
+        Sip sip = new Sip("sip:alice@twilio.com;transport=udp");
+        assertEquals("<Sip>sip:alice@twilio.com;transport=udp</Sip>", sip.toXML());
+    }
+
+    /**
+     * Test the SIP noun with a child URI noun.
+     * @throws TwiMLException
+     */
+    @Test
+    public void testSipUriNoun() throws TwiMLException {
+        Sip sip = new Sip();
+        Uri uri = new Uri("sip:alice@twilio.com;transport=udp");
+        uri.setUsername("alice");
+        uri.setPassword("hellotwilio");
+        sip.append(uri);
+        assertEquals("<Sip><Uri username=\"alice\" password=\"hellotwilio\">sip:alice@twilio.com;transport=udp</Uri></Sip>",
+                sip.toXML());
+    }
+}