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 a newer ABI revision. The Fuchsia organization 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. The Fuchsia organization 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 the Fuchsia organization, testing at tip of tree.
B = Someone who wants to make sure that an SDK is forward compatible with the a newer API level. The Fuchsia organization 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. The Fuchsia organization provides this kind of guarantee to customers whose code targets older SDKs.
See the CTS Contributing Guide.
To run example tests:
fx set core.qemu-64 --with //sdk/cts/examples/ fx test //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 should 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.
Tests that are only intended to exercise ABI may be written in any language supported for use in the Fuchsia Platform Source Tree, including Rust. This may, for example, include tests that check startup handles or the format of the VDSO.
For the most part, tests that exercise FIDL definitions and other APIs shipped with SDKs are API tests that should be written in C++. However, if this places an undue burden on test authorship (e.g., there are large frameworks needed for the test or a substantial body of appropriate existing tests that are written in Rust), we can make exceptions. Note the following:
If you do not use C++, your API will not undergo build time compatibility testing. This places a burden on anyone trying to deploy an SDK, because changes to your API are more likely to break compilation of petal code.
If there are large test frameworks or libraries that you need to use to write tests for public APIs, and they are only written in a language that is not officially supported for SDK users (see the Fuchsia language policy doc), that means that there is a form of testing that you need for exercising developer use cases that you are not providing to developers. Consider whether those test frameworks should be provided in a language that is supported for end-developers.
There will be a high bar for language exceptions for teams that wish to use other languages only because of unfamiliarity with C++. We encourage API developers to understand how end-developers use their APIs.
For information about exceptions to the C++-only policy, file a bug in the CTS bug component.
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, file a bug in the CTS bug component to reach out to the team to discuss it.
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?
I added a CTS test. How long until it is running in CQ?
For questions and clarification on this document, please reach out to this directory's owners or file a bug in the CTS bug component.