Testing overview

Zulip takes pride in its extensive, carefully designed test suites. For example, test-backend runs a complete test suite (~98% test coverage; 100% on core code) for the Zulip server in under a minute on a fast laptop; very few webapps of similar scope can say something similar.

This page focused on the mechanics of running automated tests in a development environment; you may also want to read about our testing philosophy and continuous integration setup.

Manual testing with a web browser is primarily discussed in the docs on using the development environment.

Running tests

Zulip tests must be run inside a Zulip development environment; if you’re using Vagrant, you may need to enter it with vagrant ssh.

You can run all of the test suites (similar to our continuous integration) as follows:


However, you will rarely want to do this while actively developing, because it takes a long time. Instead, your edit/refresh cycle will typically involve running subsets of the tests with commands like these:

./tools/lint zerver/lib/actions.py # Lint the file you just changed
./tools/test-backend zerver.tests.test_markdown.MarkdownTest.test_inline_youtube
./tools/test-backend MarkdownTest # Run `test-backend --help` for more options
./tools/test-js-with-puppeteer 07-navigation.js
./tools/test-js-with-node utils.js

The commands above will all run in just a few seconds. Many more useful options are discussed in each tool’s documentation (e.g. ./tools/test-backend --help).

Major test suites

Zulip has a handful of major tests suite that every developer will eventually work with, each with its own page detailing how it works:

  • Linters: Our dozen or so linters run in parallel.

  • Django: Server/backend Python tests.

  • Node: JavaScript tests for the frontend run via node.js.

  • Puppeteer: End-to-end UI tests run via a Chromium browser.

Other test suites

Additionally, Zulip also has about a dozen smaller tests suites:

  • tools/test-migrations: Checks whether the zerver/migrations migration content the models defined in zerver/models.py. See our schema migration documentation for details on how to do database migrations correctly.

  • tools/test-documentation: Checks for broken links in this ReadTheDocs documentation site.

  • tools/test-help-documentation: Checks for broken links in the /help user documentation site, and related pages.

  • tools/test-api: Tests that the API documentation at /api actually works; the actual code for this is defined in zerver/openapi/python_examples.py.

  • test-locked-requirements: Verifies that developers didn’t forget to run tools/update-locked-requirements after modifying requirements/*.in. See our dependency documentation for details on the system this is verifying.

  • tools/check-capitalization: Checks whether translated strings (aka user-facing strings) correctly follow Zulip’s capitalization conventions. This requires some maintenance of an exclude list (tools.lib.capitalization.IGNORED_PHRASES) of proper nouns mentioned in the Zulip project, but helps a lot in avoiding new strings being added that don’t match our style.

  • tools/check-frontend-i18n: Checks for a common bug in Handlebars templates, of using the wrong syntax for translating blocks containing variables.

  • ./tools/test-run-dev: Checks that run-dev.py starts properly; this helps prevent bugs that break the development environment.

  • ./tools/test-queue-worker-reload: Verifies that Zulip’s queue processors properly reload themselves after code changes.

  • ./tools/setup/optimize-svg: Checks whether all integration logo SVG graphics are optimized. logos are properly optimized for size (since we’re not going to edit third-party logos, this helps keep the Zulip codebase from getting huge).

  • ./tools/test-tools: Automated tests for various parts of our development tooling (mostly various linters) that are not used in production.

Each of these has a reason (usually, performance or a need to do messy things to the environment) why they are not part of the handful of major test suites like test-backend, but they all contribute something valuable to helping keep Zulip bug-free.

Internet access inside test suites

As a policy matter, the Zulip test suites should never make outgoing HTTP or other network requests. This is important for 2 major reasons:

  • Tests that make outgoing Internet requests will fail when the user isn’t on the Internet.

  • Tests that make outgoing Internet requests often have a hidden dependency on the uptime of a third-party service, and will fail nondeterministically if that service has a temporary outage. Nondeterministically failing tests can be a big waste of developer time, and we try to avoid them wherever possible.

As a result, Zulip’s major test suites should never access the Internet directly. Since code in Zulip does need to access the Internet (e.g. to access various third-party APIs), this means that the Zulip tests use mocking to basically hardcode (for the purposes of the test) what responses should be used for any outgoing Internet requests that Zulip would make in the code path being tested.

This is easy to do using test fixtures (a fancy word for fixed data used in tests) and the mock.patch function to specify what HTTP response should be used by the tests for every outgoing HTTP (or other network) request. Consult our guide on mocking to learn how to mock network requests easily; there are also a number of examples throughout the codebase.

We partially enforce this policy in the main Django/backend test suite by overriding certain library functions that are used in outgoing HTTP code paths (httplib2.Http().request, requests.request, etc.) to throw an exception in the backend tests. While this is enforcement is not complete (there a lot of other ways to use the Internet from Python), it is easy to do and catches most common cases of new code dependning on Internet access.

This enforcement code results in the following exception:

File "tools/test-backend", line 120, in internet_guard
  raise Exception("Outgoing network requests are not allowed in the Zulip tests."
Exception: Outgoing network requests are not allowed in the Zulip tests.

Documentation tests

The one exception to this policy is our documentation tests, which will attempt to verify that the links included in our documentation aren’t broken. Those tests end up failing nondeterministically fairly often, which is unfortunate, but there’s simply no other correct way to verify links other than attempting to access them. The compromise we’ve implemented is that in CI, these tests only verify links to websites controlled by the Zulip project (zulip.com, our GitHub, our ReadTheDocs), and not links to third-party websites.