node tests: Improve topic_list tests.

We test a little deeper now, covering rebuild (albeit mostly with
stubs) and active_stream_id.

frontend_tests/node_tests/topic_list.js

@@ -1,8 +1,10 @@
 set_global('$', global.make_zjquery());
 
+set_global('narrow_state', {});
 set_global('stream_data', {});
 set_global('unread', {});
 set_global('muting', {});
+set_global('stream_popover', {});
 set_global('templates', {});
 
 zrequire('hash_util');
@@ -12,8 +14,6 @@ zrequire('topic_list');
 
 (function test_topic_list_build_widget() {
     var stream_id = 555;
-    var active_topic = "testing";
-    var max_topics = 5;
 
     topic_data.reset();
     topic_data.add_message({
@@ -22,6 +22,12 @@ zrequire('topic_list');
         message_id: 400,
     });
 
+    stream_popover.hide_topic_popover = function () {};
+
+    narrow_state.topic = function () {
+        return 'testing';
+    };
+
     unread.num_unread_for_topic = function () {
         return 3;
     };
@@ -76,7 +82,7 @@ zrequire('topic_list');
 
     assert.equal(topic_list.active_stream_id(), undefined);
 
-    var widget = topic_list.build_widget(parent_elem, stream_id, active_topic, max_topics);
+    var widget = topic_list.rebuild(parent_elem, stream_id);
 
     assert(widget.is_for_stream(stream_id));
     assert.equal(widget.get_parent(), parent_elem);

static/js/topic_list.js

@@ -169,6 +169,8 @@ exports.rebuild = function (stream_li, stream_id) {
     var active_topic = narrow_state.topic();
     exports.remove_expanded_topics();
     active_widget = exports.build_widget(stream_li, stream_id, active_topic, max_topics);
+
+    return active_widget; // used for testing
 };
 
 // For zooming, we only do topic-list stuff here...let stream_list