JavaScript unit tests

As an alternative to the black-box whole-app testing, you can unit test individual JavaScript files.

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.

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.

Handling dependencies in unit tests

The following scheme helps avoid tests leaking globals between each other.

You want to categorize each module as follows:

  • 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, please use a pattern like this:

set_global('page_params', {
    email: ''

// then maybe further down = '';

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 smell that the other module might be lacking in cohesion, but that code might be outside your jurisdiction. 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.