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# hololink::module::TEST_ONLY

> Value of an interface's release_version that marks it as existing only for testing.

Value of an interface's `release_version` that marks it as existing only for testing.

```cpp showLineNumbers={false}
constexpr const char * hololink::module::TEST_ONLY = "test-only"
```

A [`TEST_ONLY`](testonly) interface exists to exercise the framework itself, for example a stub module's service or a fixture that records what a callback received. Applications and examples must not use one: it may change or be deleted at any time, without notice.

[`TEST_ONLY`](testonly) interfaces never appear in `INTERFACES.md`.