Running the tests

For running tests GRR uses the pytest framework.


Make sure you have correctly set-up the development environment, especially the part about installing the grr-response-test package.

This setup is sufficient for running most of the tests. However, GRR also has a UI component written in Angular. For testing that part we use Selenium and ChromeDriver which need to be installed first. You can skip this part if you do not need to execute UI tests but we strongly recommend to run them as well.

On Debian-based distros simply install chromium-driver package:

sudo apt install chromium-driver

If there is no chromium-driver available in your repositories you may try installing Chromium browser and then downloading latest chromium-driver binary from the official website. After downloading unpack it somewhere and add it to your $PATH or just move it to /usr/bin.

Running the whole test suite

To run all the tests, navigate to the root GRR directory and simply execute:


This will automatically discover and execute all test cases.

Running tests in parallel

To use pytest to run tests in parallel, install the pytest-xdist plugin

pip install pytest-xdist

and run

pytest -n <number of cores to use>

Running the tests selectively

Running all the tests is reasonable when you want to test everything before publishing your code, but it is not feasible during development. Usually you just want to execute only tests in a particular directory, like so:

pytest grr/server/aff4_objects

Or just a particular file:

pytest grr/server/aff4_objects/

Or just a particular test class:

pytest grr/server/aff4_objects/

Or even just a single test method:

pytest grr/server/aff4_objects/

Ignoring test cases

Some kind of tests are particularly slow to run. For example, all UI tests are based on running a real web browser instance and simulating its actions which is painfully sluggish and can be very annoying if we want to test non-UI code.

In this case we can skip all tests in particular directory using the --ignore flag, e.g.:

pytest --ignore=grr/gui/selenium_tests

This will run all the tests except the Selenium ones.


Benchmarks are not really testing the code correctness so there is no point in running them every time we want to publish our code. This is why the test suite will not run them by default. However, sometimes they can be useful for testing the performance and sanity of our system.

In order to run the test suite including the benchmarks, pass the --benchmark option to the test runner:

pytest --benchmark


If our tests are failing and we need to fix our code the Python Debugger can come in handy.

If you run pytest with --pdb flag then upon a failure the program execution will be halted and you will be dropped into the PDB shell where you can investigate the problem in the environment it occurred.

If you set breakpoints in your code manually using pdb.set_trace() you will notice a weird behaviour when running your tests. This is because pytest intercepts the standard input and output writes, breaking the PDB shell. To deal with this behaviour simply run tests with -s flag - it will prevent pytest from doing that.

More information

The functionalities outlined in this guide are just a tip of the pytest capabilities. For more information consult pytest’s man page, check pytest --help or visit the pytest homepage.