This is a companion library to the adjacent standalone-test library. Individual test modules can use this library instead of that one so that they can be built into either of two kinds of tests:
A standalone test executable launched directly by userboot.
Other test executables that run on full-fledged Fuchsia systems.
Test code uses this library to be flexible and adapt at runtime to either situation so the individual test modules don‘t have to be recompiled separately for the two cases. Each maybe_standalone::Get* API corresponds to a similar API in standalone::Get* from the companion standalone-test library but it can return a null result where the standalone::Get* function always returns a valid result (or panics). Flexible test code skips tests or otherwise changes behavior that it can’t do outside the standalone test context.
A standalone test executable explicitly depends on standalone-test (and minimizes its other dependencies, such as avoiding fdio). This causes any modules (e.g. source_set() targets) in its deps that themselves use maybe_standalone APIs to get valid results from those calls. Such modules should take care to keep their own dependencies minimal as well.
Flexible test modules use this maybe-standalone library but do not refer to the standalone-test library directly. When built into a different test executable that doesn't use standalone-test, their maybe_standalone calls will return their null result values.