Testing and writing tests


Zulip has a full test suite that includes many components. The most important components are documented in depth in their own sections:

This document covers more general testing issues, such as how to run the entire test suite, how to troubleshoot database issues, how to manually test the front end, etc.

We also document how to manually test the app.

Running tests

Zulip tests must be run inside a Zulip development environment; if you’re using Vagrant, you will need to enter the Vagrant environment before running the tests:

vagrant ssh
cd /srv/zulip

Then, to run the full Zulip test suite, do this:


This runs the linter (tools/lint) plus all of our test suites; they can all be run separately (just read tools/test-all to see them). You can also run individual tests which can save you a lot of time debugging a test failure, e.g.:

./tools/lint # Runs all the linters in parallel
./tools/test-backend zerver.tests.test_bugdown.BugdownTest.test_inline_youtube
./tools/test-backend BugdownTest # Run `test-backend --help` for more options
./tools/test-js-with-casper 09-navigation.js
./tools/test-js-with-node utils.js

The above setup instructions include the first-time setup of test databases, but you may need to rebuild the test database occasionally if you’re working on new database migrations. To do this, run:


Other test suites

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 maintainance 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.

Possible testing issues

  • When running the test suite, if you get an error involving Git that looks like this:

        gitlint| An error occurred while executing '/usr/bin/git rev-list --max-count=-1 upstream/master..HEAD': b"fatal: ambiguous argument 'upstream/master..HEAD': unknown revision or path not in the working tree.\nUse '--' to separate paths from revisions, like this:\n'git <command> [<revision>...] -- [<file>...]'"

    … then you may need to connect the Zulip upstream repository with the following command:

      git remote add -f upstream https://github.com/zulip/zulip.git
  • When running casper tests (./tools/test-js-with-casper), if you get an error like this:

Running node_modules/.bin/casperjs  test /srv/zulip/frontend_tests/casper_tests/00-realm-creation.js
  var err = this._handle.spawn(options);

TypeError: Bad argument

… it means that phantomjs is not installed. You can install it by running the following commands.

cd node_modules/phantomjs-prebuilt
node install.js

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.

Schema and initial data changes

If you change the database schema or change the initial test data, you have to regenerate the pristine test database by running tools/do-destroy-rebuild-test-database.

Wiping the test databases

You should first try running: tools/do-destroy-rebuild-test-database

If that fails you should try to do:

sudo -u postgres psql
> DROP DATABASE zulip_test;
> DROP DATABASE zulip_test_template;

and then run tools/do-destroy-rebuild-test-database

Recreating the postgres cluster


This is irreversible! Do it with care and never do this anywhere in production.

If your postgres cluster (collection of databases) gets totally trashed permissions-wise, and you can’t otherwise repair it, you can recreate it. On Ubuntu:

sudo pg_dropcluster --stop 9.1 main
sudo pg_createcluster --locale=en_US.utf8 --start 9.1 main

Local browser testing (local app + web browser)

This section is about troubleshooting your local development environment.

There is a separate manual testing doc that enumerates things you can test as part of manual QA.

Clearing the development database

You can use:


to drop the database on your development environment and repopulate your it with the Shakespeare characters and some test messages between them. This is run automatically as part of the development environment setup process, but is occasionally useful when you want to return to a clean state for testing.

JavaScript manual testing

debug.js has some tools for profiling JavaScript code, including:

  • `print_elapsed_time`: Wrap a function with it to print the time that function takes to the JavaScript console.

  • `IterationProfiler`: Profile part of looping constructs (like a for loop or $.each). You mark sections of the iteration body and the IterationProfiler will sum the costs of those sections over all iterations.

Chrome has a very good debugger and inspector in its developer tools. Firebug for Firefox is also pretty good. They both have profilers, but Chrome’s is a sampling profiler while Firebug’s is an instrumenting profiler. Using them both can be helpful because they provide different information.