node tests: Add test_render_windows().

frontend_tests/node_tests/message_list_view.js

@@ -1,6 +1,14 @@
+set_global('$', global.make_zjquery());
+set_global('document', 'document-stub');
+
 zrequire('util');
 zrequire('XDate', 'node_modules/xdate/src/xdate');
-var MessageListView = zrequire('message_list_view');
+zrequire('Filter', 'js/filter');
+zrequire('FetchStatus', 'js/fetch_status');
+zrequire('MessageListView', 'js/message_list_view');
+zrequire('message_list');
+
+var noop = function () {};
 
 set_global('page_params', {
   twenty_four_hour_time: false,
@@ -25,6 +33,18 @@ set_global('timerender', {
     },
 });
 
+set_global('rows', {
+    get_table: function () {
+        return {
+            children: function () {
+                return {
+                    detach: noop,
+                };
+            },
+        };
+    },
+});
+
 (function test_merge_message_groups() {
     // MessageListView has lots of DOM code, so we are going to test the message
     // group mearging logic on its own.
@@ -339,3 +359,119 @@ set_global('timerender', {
     }());
 
 }());
+
+(function test_render_windows() {
+    // We only render up to 400 messages at a time in our message list,
+    // and we only change the window (which is a range, really, with
+    // start/end) when the pointer moves outside of the window or close
+    // to the edges.
+
+    var view = (function make_view() {
+        var table_name = 'zfilt';
+        var filter = new Filter();
+        var opts = {};
+
+        var list = new message_list.MessageList(table_name, filter, opts);
+        var view = list.view;
+
+        // Stub out functionality that is not core to the rendering window
+        // logic.
+        list.unmuted_messages = function (messages) {
+            return messages;
+        };
+
+        // We don't need to actually render the DOM.  The windowing logic
+        // sits above that layer.
+        view.render = noop;
+        view.rerender_preserving_scrolltop = noop;
+
+        return view;
+    }());
+
+    var list = view.list;
+
+    (function test_with_empty_list() {
+        // The function should early exit here.
+        var rendered = view.maybe_rerender();
+        assert.equal(rendered, false);
+    }());
+
+    var messages;
+
+    function reset_list(opts) {
+        messages = _.map(_.range(opts.count), function (i) {
+            return {
+                id: i,
+            };
+        });
+        list.selected_idx = function () { return 0; };
+        list.clear();
+
+        list.add_messages(messages, {});
+    }
+
+
+    function verify_no_move_range(start, end) {
+        // In our render window, there are up to 300 positions in
+        // the list where we can move the pointer without forcing
+        // a re-render.  The code avoids hasty re-renders for
+        // performance reasons.
+        _.each(_.range(start, end), function (idx) {
+            list.selected_idx = function () { return idx; };
+            var rendered = view.maybe_rerender();
+            assert.equal(rendered, false);
+        });
+    }
+
+    function verify_move(idx, range) {
+        var start = range[0];
+        var end = range[1];
+
+        list.selected_idx = function () { return idx; };
+        var rendered = view.maybe_rerender();
+        assert.equal(rendered, true);
+        assert.equal(view._render_win_start, start);
+        assert.equal(view._render_win_end, end);
+    }
+
+    reset_list({count: 51});
+    verify_no_move_range(0, 51);
+
+    reset_list({count: 450});
+    verify_no_move_range(0, 350);
+
+    verify_move(350, [150, 450]);
+    verify_no_move_range(200, 400);
+
+    verify_move(199, [0, 400]);
+    verify_no_move_range(50, 350);
+
+    verify_move(350, [150, 450]);
+    verify_no_move_range(200, 400);
+
+    verify_move(199, [0, 400]);
+    verify_no_move_range(0, 350);
+
+    verify_move(400, [200, 450]);
+
+    reset_list({count: 800});
+    verify_no_move_range(0, 350);
+
+    verify_move(350, [150, 550]);
+    verify_no_move_range(200, 500);
+
+    verify_move(500, [300, 700]);
+    verify_no_move_range(350, 650);
+
+    verify_move(650, [450, 800]);
+    verify_no_move_range(500, 750);
+
+    verify_move(499, [299, 699]);
+    verify_no_move_range(349, 649);
+
+    verify_move(348, [148, 548]);
+    verify_no_move_range(198, 398);
+
+    verify_move(197, [0, 400]);
+    verify_no_move_range(0, 350);
+}());