node tests: Add more direct tests for typeahead.

Our legacy unit tests do kind of deep testing; we
want to test get_emoji_matcher more directly.

frontend_tests/node_tests/typeahead.js

@@ -0,0 +1,55 @@
+const typeahead = zrequire('typeahead', 'shared/js/typeahead');
+
+// The data structures here may be different for
+// different apps; the only key thing is we look
+// at emoji_name and we'll return the entire structures.
+
+const emoji_japanese_post_office = {
+    emoji_name: 'japanese_post_office',
+    url: 'TBD',
+};
+
+const emoji_panda_face = {
+    emoji_name: 'panda_face',
+    emoji_code: '1f43c',
+};
+
+const emoji_smile = {
+    emoji_name: 'smile',
+};
+
+const emoji_tada = {
+    emoji_name: 'tada',
+    random_field: 'whatever',
+};
+
+const emojis = [
+    emoji_japanese_post_office,
+    emoji_panda_face,
+    emoji_smile,
+    emoji_tada,
+];
+
+run_test('get_emoji_matcher', () => {
+    function assert_matches(query, expected) {
+        const matcher = typeahead.get_emoji_matcher(query);
+        assert.deepEqual(
+            _.filter(emojis, matcher),
+            expected
+        );
+    }
+
+    assert_matches('notaemoji', []);
+    assert_matches('da_', []);
+    assert_matches('da ', []);
+
+    assert_matches('da', [emoji_panda_face, emoji_tada]);
+    assert_matches('panda ', [emoji_panda_face]);
+    assert_matches('smil', [emoji_smile]);
+    assert_matches('mile', [emoji_smile]);
+
+    assert_matches(
+        'japanese_post_', [emoji_japanese_post_office]);
+    assert_matches(
+        'japanese post ', [emoji_japanese_post_office]);
+});