JavaScript/TypeScript unit tests

Our node-based unit tests system is the preferred way to test JavaScript/TypeScript code in Zulip. We prefer it over the Casper black-box whole-app testing, system since it is much (>100x) faster and also easier to do correctly than the Casper system.

You can run tests as follow:


The JS unit tests are written to work with node. You can find them in frontend_tests/node_tests. Here is an example test from frontend_tests/node_tests/stream_data.js:

(function test_get_by_id() {
    var id = 42;
    var sub = {
        name: 'Denmark',
        subscribed: true,
        color: 'red',
        stream_id: id
    stream_data.add_sub('Denmark', sub);
    sub = stream_data.get_sub('Denmark');
    assert.equal(sub.color, 'red');
    sub = stream_data.get_sub_by_id(id);
    assert.equal(sub.color, 'red');

The names of the node tests generally align with the names of the modules they test. If you modify a JS module in static/js you should see if there are corresponding test in frontend_tests/node_tests. If there are, you should strive to follow the patterns of the existing tests and add your own tests.

How the node tests work

Unlike the casper unit tests, which use the phantomjs browser connected to a running Zulip deveopment server, our node unit tests don’t have a browser, don’t talk to a server, and generally don’t use a complete virtual DOM (a handful of tests use the jsdom library for this purpose) because those slow down the tests a lot, and often don’t add much value.

Instead, the preferred model for our unit tests is to mock DOM manipulations (which in Zulip are almost exclusively done via jQuery) using a custom library zjquery.

The unit test file for zjquery is designed to be also serve as nice documentation for how to use zjquery, and is highly recommended reading for anyone working on or debugging the Zulip node tests.

Conceptually, the zjquery library provides minimal versions of most jQuery DOM manipulation functions, and has a convenient system for letting you setup return values for more complex functions. For example, if the code you’d like to test calls $obj.find(), you can use $obj.set_find_results(selector, $value) to setup zjquery so that calls to $obj.find(selector) will return $value. See the unit test file for details.

This process of substituting jQuery functions with our own code for testing purposes is known as “stubbing”. zjquery does not stub all possible interactions with the dom, as such, you may need to write out the stub for a function you’re calling in your patch. Typically the stub is just placed in the test file, to prevent bloating of zjquery with functions that are only used in a single test.

If you need to stub, you will see an error of this form: Error: You must create a stub for $("#foo").bar

The zjquery library itself is only about 500 lines of code, and can also be a useful resource if you’re having trouble debugging DOM access in the unit tests.

It is typically a good idea to figure out how to stub a given function based on how other functions have been stubbed in the same file.

Handling dependencies in unit tests

The other big challenge with doing unit tests for a JavaScript project is that often one wants to limit the scope the production code being run, just to avoid doing extra setup work that isn’t relevant to the code you’re trying to test. For that reason, each unit test file explicitly declares all of the modules it depends on, with a few different types of declarations depending on whether we want to:

  • Exercise the module’s real code for deeper, more realistic testing?
  • Stub out the module’s interface for more control, speed, and isolation?
  • Do some combination of the above?

For all the modules where you want to run actual code, add statements like the following toward the top of your test file:

zrequire('Filter', 'js/filter');

For modules that you want to completely stub out, use a pattern like this:

set_global('page_params', {
    email: ''

// then maybe further down = '';

One can similarly stub out functions in a module’s exported interface with either noop functions or actual code.

Finally, there’s the hybrid situation, where you want to borrow some of a module’s real functionality but stub out other pieces. Obviously, this is a pretty strong code smell that the other module might be lacking in cohesion, but sometimes it’s not worth going down the rabbit hole of trying to improve that. The pattern here is this:

// Import real code.

// And later... = function () {
    return 'office';

Creating new test modules

The test runner (index.js) automatically runs all .js files in the frontend_tests/node directory, so you can simply start editing a file in that directory to create a new test.

The nodes tests rely on JS files that use the module pattern. For example, to test the foobar.js file, you would first ensure that code like below is at the bottom of foobar.js:

if (typeof module !== 'undefined') {
    module.exports = foobar;

This means foobar.js follow the CommonJS module pattern, so it can be required in Node.js, which runs our tests.

Coverage reports

You can automatically generate coverage reports for the JavaScript unit tests like this:

    tools/test-js-with-node --coverage

If tests pass, you will get instructions to view coverage reports in your browser.

Note that modules that we don’t test at all aren’t listed in the report, so this tends to overstate how good our overall coverage is, but it’s accurate for individual files. You can also click a filename to see the specific statements and branches not tested. 100% branch coverage isn’t necessarily possible, but getting to at least 80% branch coverage is a good goal.

The overall project goal is to get to 100% node test coverage on all data/logic modules (UI modules are lower priority for unit testing).