node tests: Bring list_cursor to 100% coverage.

We had some indirect coverage of this already, so
this mostly focuses on error cases and corner
cases.

frontend_tests/node_tests/list_cursor.js

@@ -0,0 +1,80 @@
+zrequire('list_cursor');
+
+set_global('blueslip', global.make_zblueslip());
+
+run_test('config errors', () => {
+    blueslip.set_test_data('error', 'Programming error');
+    list_cursor({});
+});
+
+function basic_conf() {
+    const list = {
+        scroll_container_sel: 'whatever',
+        find_li: () => {},
+        first_key: () => {},
+        prev_key: () => {},
+        next_key: () => {},
+    };
+
+    const conf = {
+        list: list,
+        highlight_class: 'highlight',
+    };
+
+    return conf;
+}
+
+run_test('misc errors', () => {
+    const conf = basic_conf();
+
+    const cursor = list_cursor(conf);
+
+    // Test that we just ignore empty
+    // lists for unknown keys.
+    conf.list.find_li = (opts) => {
+        assert.equal(opts.key, 'nada');
+        assert.equal(opts.force_render, true);
+        return [];
+    };
+
+    cursor.get_row('nada');
+
+    blueslip.set_test_data('error', 'Caller is not checking keys for list_cursor.go_to');
+    cursor.go_to(undefined);
+
+    blueslip.set_test_data('error', 'Cannot highlight key for list_cursor: nada');
+    cursor.go_to('nada');
+
+    blueslip.clear_test_data();
+    cursor.prev();
+    cursor.next();
+});
+
+run_test('single item list', () => {
+    const conf = basic_conf();
+    const cursor = list_cursor(conf);
+
+    const valid_key = '42';
+    const li_stub = {
+        length: 1,
+        addClass: () => {},
+    };
+
+    cursor.adjust_scroll = () => {};
+
+    conf.list.find_li = () => {
+        return li_stub;
+    };
+
+    cursor.go_to(valid_key);
+
+    // Test prev/next, which should just silently do nothing.
+    // (Our basic_conf() has prev_key and next_key return undefined.)
+    blueslip.clear_test_data();
+    cursor.prev();
+    cursor.next();
+
+    // The next line is also a noop designed to just give us test
+    // coverage.
+    cursor.go_to(valid_key);
+});

tools/test-js-with-node

@@ -45,6 +45,7 @@ enforce_fully_covered = {
     'static/js/filter.js',
     'static/js/hash_util.js',
     'static/js/keydown_util.js',
+    'static/js/list_cursor.js',
     'static/js/markdown.js',
     'static/js/message_store.js',
     'static/js/muting.js',