Extract jabber-xml-parse-next-stanza, and test it

Move the functionality of reading the next complete stanza into a
separate function, and add some test cases for it.  I'd like to get rid
of jabber-xml-skip-tag-forward at some point, so a good first step
towards that should be moving calls to it into a function that's easy to
test in isolation.

jabber-core.el

@@ -899,10 +899,7 @@ DATA is any sexp."
 	 (while (search-forward-regexp " \\w+=''" nil t)
            (replace-match "")))
        
-       (setq xml-data (and (catch 'unfinished
-			     (jabber-xml-skip-tag-forward)
-			     (> (point) (point-min)))
-			   (xml-parse-region (point-min) (point))))
+       (setq xml-data (jabber-xml-parse-next-stanza))
 
        while xml-data
        do

jabber-xml.el

@@ -133,6 +133,17 @@ enough for us."
    (t
     (throw 'unfinished nil))))
 
+(defun jabber-xml-parse-next-stanza ()
+  "Parse the first XML stanza in the current buffer.
+Parse and return the first complete XML element in the buffer,
+leaving point at the end of it.  If there is no complete XML
+element, return `nil'."
+  (and (catch 'unfinished
+	 (goto-char (point-min))
+	 (jabber-xml-skip-tag-forward)
+	 (> (point) (point-min)))
+       (xml-parse-region (point-min) (point))))
+
 (defsubst jabber-xml-node-name (node)
   "Return the tag associated with NODE.
 The tag is a lower-case symbol."

tests/Makefile.am

@@ -2,5 +2,5 @@
 # check" or "make distcheck" to work with earlier versions.
 LOG_COMPILER = env top_builddir=$(top_builddir) $(EMACS) -batch -L $(top_builddir) -L $(top_srcdir) -L $(srcdir) -l
 TESTS = load-all.el skip-tag-forward.el history.el jabberd.el nick-change-fail.el
-TESTS += caps-hash.el
+TESTS += caps-hash.el parse-next-stanza.el
 dist_noinst_DATA = $(TESTS)

tests/parse-next-stanza.el

@@ -0,0 +1,18 @@
+;; Tests for jabber-xml-parse-next-stanza
+
+(require 'jabber-xml)
+
+(defun parse-it (text)
+  (with-temp-buffer
+    (insert text)
+    (jabber-xml-parse-next-stanza)))
+
+(unless (equal
+	 (parse-it "<presence from='foo@example.com/resource' type='unavailable' to='bar@example.com'/>")
+	 '((presence ((from . "foo@example.com/resource") (type . "unavailable") (to . "bar@example.com")))))
+  (error "Testcase 1 failed"))
+
+(unless (equal
+	 (parse-it "<presence from='foo@example.com/resource' ")
+	 nil)
+  (error "Testcase 2 failed"))