androidxannotationTestOnly

androidx.annotation.TestOnly is a marker annotation in the AndroidX Annotation library used to indicate that a program element is intended only for test code. It can be applied to methods, fields, constructors, or classes to signal that they should not be used from production or non-test code.

The primary purpose of TestOnly is to aid developers and static analysis tools by documenting and enforcing a testing boundary. It is not a runtime security or access control mechanism; the annotation itself does not prevent access or modify behavior at runtime. Instead, it relies on tooling such as lint checks to warn when a test-only element is used outside of test code. In practice, test-only code is typically kept in test sourcesets, and production builds should avoid referencing such APIs.

Usage is straightforward: annotate the relevant element with @TestOnly, and ensure your project includes the AndroidX annotation library. For example, a test-only helper method might be declared as @TestOnly void resetForTests() { ... }. The annotation can also aid library authors in signaling that certain internal APIs are not supported for public use.

In addition to TestOnly, other testing-related annotations like @VisibleForTesting are commonly used to express related intent about visibility and usage constraints. While TestOnly communicates test-only intent, it should not be relied upon to enforce behavior; developers should prefer proper separation of test code from production code and use tooling to catch violations.

See also: androidx.annotation, @VisibleForTesting, lint.