Testing principles

Testing is central to the continuous integration processes that Fuchsia contributors practice to sustain quality and velocity. Good tests become an asset to the team, while bad tests can turn into a liability.

This document reviews topics related to testing on Fuchsia, and provides references to additional resources. This document assumes that you are familiarized with general software testing concepts.

Fuchsia platform testing should serve the goals of the project and align with Fuchsia's architectural principles:

  • Secure: Tests are subject to the same security, isolation, and hermeticity mechanisms that apply to production software. Tests leverage those same mechanisms for their benefit. The security properties of the system are testable.
  • Updatable: It's important to test the stable interfaces between components and other parts of the stable Fuchsia System Interface. If components under tests change or are entirely replaced, tests that only exercise interfaces between components should continue to work. Tests that are outside of Fuchsia tree should not assume implementation details of platform components.
  • Inclusive: Testing frameworks and testing guides should either not assume that the developer is using a particular runtime, programming language, or hardware, or alternatively demonstrate that developers can make their own choices, such as by providing support in multiple distinct languages and making it easy to bring up new language support. Tests for public and open source Fuchsia code should themselves be public and open source.
  • Pragmatic: When the principles presented above are in conflict with each other or with important near-term goals, it’s ok to make pragmatic choices. It is usually not important to meet an arbitrary bar, for instance a fixed percentage of test coverage, or a particular mix of unit, integration, and system tests.

How is testing different on Fuchsia?

Operating systems are complex programs

Every domain of software development and testing brings unique challenges. There are special problems and solutions to testing an operating system, as there are for testing a mobile application or server software or a spacecraft.

For instance, tests for the Zircon kernel run in a special runtime environment that makes as few assumptions as possible that the kernel is functional, and can detect mistakes in low-level kernel code. Contrast this with typical application testing, where the tests run on some operating system that is assumed to be working.

Isolation and hermeticity

The Component Framework promotes Fuchsia’s security goals by running each component in a sandbox environment that is strictly-defined in a component manifest. It then promotes Fuchsia’s updatability goals by only allowing components to interconnect using those component capabilities that are typed as updatable contracts.

These same mechanisms of isolation and hermeticity can also be used by tests as a form of dependency injection. For instance a component under test can be provided a test double for a capability that it depends on by a test harness, making contract testing easier.

Multiple repositories

Fuchsia is a large project with many external dependencies, and builds against hundreds of other source code repositories. Multi-repository development introduces unique challenges to testing. A contributor working on the WebRTC project published a blog post detailing many of the problems and solutions that are also encountered when developing Fuchsia.

Further reading