Quick Start

To build Zircon and run unit tests, run one of the following commands:

# Build and run x64.
fx set bringup.x64 --with-base //bundles/buildbot/bringup
fx build
fx qemu

# Build and run arm64.
fx set bringup.arm64 --with-base //bundles/buildbot/bringup
fx build
fx qemu

Once the scripts finish running, you should see the Zircon shell. To run userspace tests, use the Zircon shell to run:

runtests --all

You can use runtests --all -d to see the list of tests available in the system. You can also use runtests -n <TEST_NAME> to run one specific test.

To run in-kernel tests, use the Zircon shell to run:

k ut all

Fuchsia's Get Started page has more details about how to use the Zircon shell and how to automatically build all supported architectures.

Userspace Tests

The test harness, runtests, picks up and runs all of the executables from the /boot/test and /system/test directories. If you provide a command-line argument, such as runtests -m widget_test, runtests will only run the single test requested -- in this case, widget_test.

Kernel-mode Tests

The kernel contains unit tests and diagnostics, which can be run using the k command. The output of the k command will only be shown on the console. Depending on your configuration, this might be the serial console, or the debuglog virtual terminal.

Unit tests

Many parts of the kernel have unit tests, which report success/failure automatically. These unit tests are built using the primitives provided by the kernel unit-test library. You can find these statically by searching for UNITTEST_START_TESTCASE.

These tests can be run from the shell with k ut. k ut all will run all tests or you can use k ut $TEST_NAME to run a specific test.


Many parts of the kernel provide diagnostics, whose output requires manual inspection. Some of these diagnostics are used to verify correctness (e.g. timer_diag), while others simply stress test a part of the system (e.g. timer_stress).

To run a diagnostic, simply pass its name to the k command. For example, to run the kernel's builtin benchmarks, run k bench. To find the full set of kernel diagnostics statically, search for STATIC_COMMAND. To enumerate them dynamically, run k help.

Diagnostic tests are intended to be run via serial console, or with physical access to the system. Some diagnostics may be destructive, and leave the system in a broken state.