Google celebrates Hispanic Heritage Month. See how.

Contributing Tests to CTF

This guide provides instructions on how to contribute a test to CTF.

How to write an ABI test

An ABI test is a test that verifies the ABI or runtime behavior of an API in the SDK. These tests are distributed as Fuchsia packages containing test components and run entirely on the target device.


Step 1: Create a test directory

The structure of the //sdk/ctf directory mirrors the structure of SDK artifacts. Your test should go in the same directory as the interface under test is found in an SDK. For example:

Tests for... Should go in...
Host tools //sdk/ctf/tests/tools
FIDL interfaces //sdk/ctf/tests/fidl
Libraries //sdk/ctf/tests/pkg

See existing tests under //sdk/ctf/tests for examples.

Step 2: Create your test executable

In your test directory's file, create a test executable using CTF build templates.



ctf_executable("my_test_binary") {
  deps = [ "//zircon/system/ulib/zxtest" ]
  sources = [ "" ]
  testonly = true



ctf_rustc_test("my_test_binary") {
  edition = "2021"
  source_root = "src/"
  sources = [ "src/" ]

Step 3: Create your test component

// my_test_component.cml
    include: [
        // Select the appropriate test runner shard here:
        // rust, elf, etc.
    program: {
        binary: "bin/my_test_binary",
    facets: {
        // mark your test type "cts".
        "fuchsia.test": { type: "cts" },

Wrap your executable as a Fuchsia component. CTF provides a special GN template for creating a component:

ctf_fuchsia_component("my_test_component") {
  testonly = true
  manifest = "meta/my_test_component.cml",
  deps = [ ":my_test_binary" ]

Step 4: Create your test package

CTF also provides a special GN template for creating a test package:

ctf_fuchsia_test_package("my_test") {
  package_name = "my_test"
  test_components = [ ":my_test_component" ]

Step 5: Run the test

These instructions require you to open several terminal tabs.

Tab 1: Start the Fuchsia package server

fx serve

Tab 2: Start the Fuchsia emulator

ffx emu start --headless
  • --headless disables graphical output.

For more information on configuring the emulator, see Start the Fuchsia Emulator.

Tab 3: Stream the device logs

This step is useful for debugging your test.

ffx log

Tab 4: Run the test

fx set core.x64 --with TARGET_LABEL 
fx test TARGET_LABEL # or fx test TEST_NAME 
  • -v enables verbose output.

See the section about "Debugging tips" below.

Step 6. Verify your test passes as part of the CTF release

This step involves building the CTF in the same way that our CI does when it is released, then running those CTF tests in your local checkout. It is necessary because upon release, we automatically rewrite each CTF test package's name to deduplicate it from the same package's name at HEAD (the build does not allow duplicate names) and we must verify that the test still passes after this rewrite.

Follow the instructions in Step 4 to start an emulator and a package server, then launch a new terminal and run the following command:


This command will build the CTF archive, release it to your //prebuilt/cts/test/* directory, and run the tests contained therein. After a brief pause, the test results will be printed to the terminal window.

To learn more about that script, or to run the commands manually, please see //sdk/ctf/build/scripts/verify_release/

Some common causes of test failure at this stage include:

  • The test launches one of its child components using an absolute component URL.
    • Explanation: The URL is no longer correct because the test's package was renamed.
    • Solution: Use a relative component URL instead.
  • The test is missing a dependency.
    • Explanation: It's possible that the Fuchsia system contained a different set of packages when you built and ran your test at HEAD vs as part of the CTF and that your test depended on some of those packages.
    • Solution: Make sure your test's GN target explicitly lists all of its direct dependencies as deps.

If you need additional help debugging at this step, please reach out to the CTF team by filing a bug in the CTF bug component.

Step 7. Make the test run on presubmit

This step causes the version of your test from Fuchsia's HEAD commit to run as part of Fuchsia's presumbit queue.

Add a "tests" group to your BUILD file:

group("tests") {
  testonly = true
  deps = [ ":my_test" ]

Next add this target as a dependency to the closest ancestor group("tests") target. This will ensure that your test is added to the next CTF release.

Debugging Tips

  • If your test hangs, use ffx component list -v to inspect its current state.

How to write a test for experimental FIDL

The CTF supports writing tests for FIDL interfaces that are not yet released in the SDK. This allows you to write CTF tests for your API while you are still developing it. Writing tests using the CTF framework while you develop your API ensures that your tests do not depend on any non-SDK targets.

Step 1. Ensure your FIDL is marked as experimental

Your FIDL interface should be marked with sdk_category = "experimental". If your interface is marked as public or partner, follow the steps above to write a CTF test.

fidl("fuchsia.interface") {
  sdk_category = "experimental"
  name = "fuchsia.interface"
  sources = [ "interface.fidl" ]

Step 2. Add your FIDL to the CTF allow list

The CTF verifies that its dependencies are in the SDK. To avoid build time errors, your FIDL must be added to the CTF allow list.

# //sdk/ctf/build/allowed_ctf_deps.gni

Step 3. Follow the steps above to write an ABI test

Follow the steps in the How to write an ABI test section to write an ABI test for your experimental FIDL.

Step 4. Mark your test package as experimental

The CTF includes tests based on metadata generated by ctf_fuchsia_test_package. To avoid generating this metadata (and including your test in the CTF), mark your test package with uses_experimental_fidl.

ctf_fuchsia_test_package("my_experimental_test") {
  uses_experimental_fidl = true
  test_components = [ ":my_experimental_component" ]

Step 5. Release your CTF test

When your FIDL interface is no longer experimental, release your CTF test! To release your CTF test, follow the steps in the How to write an ABI test section and delete the uses_experimental_fidl line from your ctf_fuchsia_test_package.

How to remove an ABI test

Please see the FAQ section about retiring tests.

How to disable your test

Please see the FAQ section about disabling tests.