This directory contains the Fuchsia Compatibility Test Suite (CTS). The Fuchsia CTS is a set of tests designed to provide coverage for Application Programming Interface (API) and Application Binary Interface (ABI) elements (e.g., headers, FIDL files) made available to developers via a Fuchsia SDK. It was originally proposed as RFC 0015.
The CTS exists to determine whether a build of the Fuchsia platform, running on a particular device, correctly implements (or is compatible with) the API and ABI exposed by a particular Fuchsia SDK. To put it another way, it demonstrates that the build correctly implements Fuchsia.
If a system running Fuchsia passes the CTS tests for a particular ABI revision, then its developers can have confidence that components built for that revision will work on the system, and that the system is backwards compatible with that revision.
Each release of the Fuchsia platform is bundled with a set of Software Development Kits (SDKs), which contain tools, libraries, and headers that allow developers to target Fuchsia's APIs and ABIs. We refer to the API and ABI as Platform Surface Area (or PlaSA). Each SDK will be paired with a set of CTS tests that exercise the surface area it exposes. The tests will be available in both source and binary form.
CTS tests are not comprehensive. They cannot guarantee that any component that is built against one SDK will run against any particular build of Fuchsia. CTS must, therefore, be complemented with product-specific testing.
With that in mind, the CTS can then be used to enforce compatibility in the following ways:
The CTS binary tests can be run against a device running Fuchsia to ensure that the build on that device is ABI compatible with the CTS's associated SDK. This can provide enforcement of backwards compatibility guarantees: if the CTS from a given SDK passes, that is a strong indicator (although not a conclusive one) that programs built against that SDK will continue to work. It can also provide confidence that software running on the device that is not exercised by in-tree tests, such as out-of-tree device drivers, does not change the behavior of the platform.
As a table:
| Run → Against ↓ | CTS N | CTS N + 1 |
|---|---|---|
| SDK / Product Build at version N | A | B |
| SDK / Product Build at version N + 1 | C | A |
Where:
A = Someone who wants to make sure a product build correctly implements the ABI revision they claim it does.
B = Someone who wants to make sure that a product build is forward compatible with the a newer ABI revision. Fuchsia org doesn't provide this kind of guarantee.
C = Someone who wants to make sure that a product build is backwards compatible with an older ABI revision. Fuchsia org provides this kind of guarantee to customers whose code targets older SDKs.
The CTS source tests can be built against an SDK to ensure that the SDK is API compatible with the CTS's associated SDK. Additionally, CTS contains a suite of tests for SDK host tools. These tests can provide confidence that changes to the SDK do not break developer code and workflows. For example, we can build the CTS for API version N against an SDK that contains support for API version N+1 to see if the SDK has broken API compatibility. Currently, the only SDK vendor supported by the CTS project is the Fuchsia organization itself.
As a table:
| Build → Against ↓ | CTS N | CTS N + 1 |
|---|---|---|
| SDK at version N | A | B |
| SDK at version N + 1 | C | A |
Where:
A = Someone who wants to make sure an SDK correctly implements the API level they claim it does. This includes Fuchsia org (testing at tip of tree).
B = Someone who wants to make sure that an SDK is forward compatible with the a newer API level. Fuchsia org doesn't provide this kind of guarantee.
C = Someone who wants to make sure that an SDK is backwards compatible with an older API level. Fuchsia org provides this kind of guarantee to customers whose code targets older SDKs.
This section provides guidelines on how to author CTS tests.
CTS tests are intended to provide coverage for the platform surface area, including ABI, API, and tooling exposed through the SDK. We have a variety of guidelines to encourage this; rules are provided in boldface text below. Subsequent sections add more detail to these rules.
CTS tests must be stored in //sdk/cts unless specific permission is given from the CTS team for the test to be stored elsewhere. There is no such restriction for test infrastructure (e.g., the zxtest library), but we encourage discussion with the team if you have questions.
CTS tests typically target elements of the platform surface area directly. If one fails, it should be clear which parts of the platform surface area were triggered, and what the changed outcome is. As a result of this rule, typically, the amount of application logic in a test is small.
CTS tests should target all of the testable assertions presented in the documentation for elements of the platform surface area under test. For example, if we have a class fit::basic_string_view, and it has a method size that is documented to return the size of the string_view, we would have a test that creates a string_view, calls the size method, and asserts that the return value is correct.
CTS tests developed in fuchsia.git must conform to all requirements for code checked into fuchsia.git, including code review, style, language level, and so on.
CTS tests may rely on anything in an SDK. We also accept non-test code submissions that only use platform surface area elements exposed via an SDK; test libraries such as zxtest fall under this rule. We expect developers to be aware that relying on anything other than the surface area under test makes a CTS test more subject to unrelated failure, and to write code accordingly. For example, the zxtest library does not rely on synchronization, so failures in synchronization mechanisms cannot cause all zxtest-based tests to fail.
Tests should reflect best practices about the usage of a given API. Informally, if an end developer were to see the test, and copy its usage of the API, the test author would believe that developer would be using the API correctly. Tests should, to the extent possible, not depend on undocumented, application-specific invariants. In the future, in the case of widespread use of undocumented usages outside of the Fuchsia tree, we may need to support use cases that do not follow recommended usages.
CTS tests must restore the state of the system under test when the test has completed. For example, a test might make a system-wide change to set the foreground and background color of text to the same color. The colors should be reset at the end of the test. We will likely relax this restriction as we get better at writing test infrastructure; please reach out to us with concerns. Tests should not depend on the behavior of previous tests.
CTS tests must not have timeouts. Instead, timeouts should be enforced by the test infrastructure.
CTS tests should not sleep. Sleeps are common causes of flakiness in tests, as timing can vary wildly between runs depending on target hardware and system load. We recommend that developers structure code so that an explicit signal is sent when a given condition is met, rather than having part of a test wait an arbitrary amount of time for other code to finish.
CTS tests may not depend on infrastructure outside the tests, the test harness, and the system under test. For example, they should not make requests to known servers on the Internet or look for files in known locations on host operating systems.
CTS tests should avoid creating test doubles (e.g., mocks and fakes) for the internal state of the target device. The intent of the CTS is to make sure the entire device behaves correctly, not to make sure that a particular component behaves correctly in isolation.
CTS tests should exercise boundary conditions (e.g., values of 0 and MAXINT for integers, and null pointers for pointer values) as well as typical elements. This is simply to provide for better testing.
We do not encourage developers to submit stress tests or performance tests to the CTS. Such tests will be examined closely for coverage value.
The structure of the //sdk/cts directory mirrors the structure of SDK artifacts. Tests should go in the same directory as the interface under test is found in an SDK. For example:
//sdk/cts/tests/tools//sdk/cts/tests/fidl. For example, tests for fuchsia.sysmem should go in //sdk/cts/tests/fidl/fuchsia.sysmem.//sdk/cts/tests/pkg. For example, tests for async-loop should go in //sdk/cts/tests/pkg/async-loop.CTS tests target API and ABI available through externally-available SDKs. Build support ensures that tests only depend on API elements that are available via an SDK, or whitelisted for use within the CTS. All build targets must use the cts_ rule variants found in //sdk/cts/build instead of the standard fuchsia.git rules (i.e., use cts_fuchsia_component, cts_executable, and so on).
The allowlist for non-SDK code can be found in //sdk/cts/build/allowed_cts_deps.gni. Test authors who believe they need an additional inclusion should reach out to the OWNERS of this directory.
To run example tests, append --with //sdk/cts to fx set eg, fx set core.qemu-64 --with //sdk/cts
Next, run fx test //sdk/cts/examples/
For example tests, see //sdk/cts/examples.
Tests for particular headers must be written in a language that supports that header. C headers currently target C11 and C++11 and above. C++ headers currently target C++14 and above. This policy may change as we build a larger test corpus and decide how to enforce C++14 compatibility.
All tests that target API must be written in a language that is supported for end developers per the Fuchsia language policy. The CTS currently only provides direct support for C++ for tests that target API.
In the future, we plan on supporting ABI-only tests that can be written in different languages (e.g., Rust) and delivered as prebuilts into the CTS.
For end-to-end tests and scripts that run on the host, we support the use of Dart (and, specifically sl4f).
Since tests are designed to exercise the SDK APIs and ABIs, dependencies on SDK elements (tools, APIs) are allowed.
See the section on build support for information on including new dependencies on first-party code.
In order to avoid relying on third party use of the SDK to test the SDK, CTS tests that run on-device do not rely on third party frameworks that rely on the SDK to build. This is why we use zxtest instead of gtest. If you want to include a third party dependency, contact the OWNERS of //sdk/cts/.
Code that runs on the host does not have this restriction.
Are there any examples of CTS tests?
Is CTS appropriate for unit tests of my service?
What is meant by compatibility in the C of CTS?
What is the compatibility window that CTS attempts to uphold?
Are CTS tests those that reach into the service or do they access the FIDL or API?
One responsibility Fuchsia.settings.display has is to change the brightness of the screen. Should the test change the brightness and then assert a response given that the brightness changed? Or should the test use an emulator to identify if the brightness actually changed?
How will we know if a test fails?
Where will CTS tests run? Emulator? Devices?
How do we get started as a rust service? Why does language matter? What level of effort might it be to get rust tests to work?
For questions and clarification on this document, please reach out to the directory's owners.