You are encouraged to add your own questions (and answers) here!
Q: How do I define a new unit test?
A: Use language-appropriate constructs, like GTest for C++. You can define a new file if need be, such as:
(in a BUILD.gn file)
executable("unittests") {
output_name = "scenic_unittests"
testonly = true
sources = ["some_test.cc"],
deps = [":some_dep"],
}
Q: What ensures it is run?
A: Tests are represented as entries in the FUCHSIA_BUILD_DIR/tests.json file
generated by GN based on arguments of fx set. The step that creates or updates
tests.json is called the gen phase of the build, and it is triggered by
fx set, fx build or explicitly by fx gen.
If fx test doesn't find your test, first check FUCHSIA_BUILD_DIR/tests.json.
In most cases, the product configuration plus the --with arguments of your
fx set commmand are missing, directly or transitively, the test that you are
attempting to run. If that's the case, just add the test GN label or a GN
label that transitively has the test as an --with argument to the fx set
command, for example:
fx set ... --with //src/sys:tests
If a newly added test is in the product configuration defined by fx set but
still doesn't show in tests.json, you may need to run fx gen or fx build
to update tests.json so that fx test knows how to run it.
Q: How do I run this unit test on a QEMU instance?
There's the easy way if your QEMU has networking, and the hard way if it doesn't.
A (with networking): In one terminal, start your QEMU instance with fx qemu -N.
Next, on another terminal, type in fx test scenic_tests.
This invocation runs all the test executables in the scenic_tests package.
A (no networking): Start a QEMU instance (fx qemu), and then manually invoke
the runtests command.
In the QEMU shell, type in run-test-component scenic_tests. The
argument is a specific directory containing the test executables.
Note Well! Without networking, the files are loaded into the QEMU instance at startup. So after rebuilding a test, you'll need to shutdown and re-start the QEMU instance to see the rebuilt test.
To exit QEMU, dm shutdown.
Q: How do I run this unit test on my development device?
A: Either manual invocation, like in QEMU, or fx test to a running
device.
Note that the booted device may not contain your binary at startup, but fx
test will build the test binary, ship it over to the device, and run it,
while piping the output back to your workstation terminal. Slick!
Make sure your device is running (hit Ctrl-D to boot an existing image) and connected to your workstation.
From your workstation, fx test scenic_tests will serially run through all
test executables contained in the scenic_tests package.
To run just one test executable, use the following command:
fx test <executable-name>
You can automatically rebuild, install, and run your tests on every source file
change with fx -i. For instance: fx -i test scenic_tests.
Q: Where are the test results captured?
A: The output is directed to your terminal.
There does exist a way to write test output into files (including a summary JSON file), which is how CQ bots collect the test output for automated runs.
Q: How to disable a test? How to find and run disabled tests?
A: There are several ways to do this. Whenever doing any of these, be sure to file a bug and reference that bug in a comment in the code that disables the test.
Tag the test as flaky
You can do this by adding "flaky" to the tags field in the
test environment. This operates
on the entire test target (which corresponds to an executable). It will prevent this target
from running on the builders in the commit queue, and enable the target on special flaky
builders that continue to run the test in CI. Be sure to note the bug in a
comment in the BUILD.gn file.
Example change.
If you want to disable only some tests that are part of a larger test target, you'll need to split the target into two GN targets, and tag one as flaky.
C++ googletest only: Prefix name with DISABLED
To disable a particular test inside of a larger test executable,
you can mark it as disabled. Disabled tests are defined by having their name
prefixed with DISABLED_. One way to find them is therefore simply git grep
DISABLED_.
If running the test outputs YOU HAVE 1 DISABLED TEST, you can also pass the
following flags to find out which test is disabled: fx run-test scenic_tests --
--gtest_list_tests --gtest_filter=*DISABLED_*.
To force-run disabled tests: fx run-test scenic_tests --
--gtest_also_run_disabled_tests.
Rust only: apply the #[ignore] attribute
To disable a particular test inside of a larger Rust test executable, you can
tag it with #[ignore]. It should be applied underneath the #[test] attribute.
Example:
#[test]
#[ignore] // TODO(fxbug.dev/NNNNN) re-enable this test when de-flaked
fn flaky_test_we_need_to_fix() { ... }
Mark test disabled
Alternatively, you may also disable an entire test executable within a
package containing several test executables. To do this, edit the BUILD.gn as
follows: tests = [ { name = "scenic_unittests", disabled = true } ]. As a
result, scenic_unittests will be put in a disabled subdirectory of
/pkgfs/packages/<package_name>/0/test, and will not be run by the CQ system.
Comment out the test
To disable a particular test inside of a larger test executable, you can comment out the code that defines that test.
Q: How do I run a bunch of tests automatically? How do I ensure all dependencies are tested?
A: Unlike the fx run-test command, the primary feature of fx test is batch
execution. See Run Fuchsia tests
for examples on how to run multiple tests or test suites together.
Additionally, you can always upload your patch to Gerrit and do a CQ dry run.
Q: How do I run this unit test in a CQ dry run?
A: Clicking on CQ dry run (aka +1) will take your change's properly defined unit test and run it on multiple bots, one for each build target (x86-64 versus arm64, release versus debug). Each job will have an output page showing all the tests that ran.
Q: How do I use some build time artifacts in my unit test?
A: The simplest artifact is just a file that is in your source directory. For
this you just need to add it to resources attribute of the package definition
of your unit test. For example, you may do something like this in your
BUILD.gn:
rustc_binary("my-great-app") {
with_unit_tests = true
...
}
test_package("my-great-app-tests") {
deps = [
":my-great-app_test",
]
resources = [
{
path = "source.zip"
dest = "testing.zip"
}
]
The file will be available as /pkg/data/testing.zip inside the environment
where the test binary will be executed.
TODO: If you want an artifact that is generated as part of the build process,
you should probably add the rule that generates the artifact to the data_deps
array of the test_package rule. But I have not tried it yet. Update this
section when you will try it :)