[carrerasdarren-cell]

Fixes: #2359

Description

Add headless coverage for the app manager's Backup action, from the real bound adapter menu through its unchanged Intent to CopyService. The tests verify that the base APK and every split reach app_backup under the expected names with their original bytes intact, and that backup preserves the sources. Production code is unchanged.

The split case covers ABI, locale and uppercase-extension/density names with distinct binary contents. Null and empty split lists provide the single-APK controls. Every case checks the actual service component, target and UNKNOWN-mode Intent, the completion broadcast, absence of failed-operation broadcasts, and the exact output filenames and bytes.

Automatic tests

• Added headless Robolectric workflow tests.
• Added separate pure function unit tests — this change covers the menu/service workflow.
• Added emulator tests — no UI elements or layouts changed.
• ./gradlew :app:testFdroidDebugUnitTest --tests com.amaze.filemanager.adapters.AppsRecyclerAdapterBackupTest — 9 passed, zero failures/errors/skips across the inherited configured SDK variants (21/28/30).

The final test source was rerun after a helper-only readability extraction. Test inputs, assertions and production behavior remained unchanged. These are actual project/Robolectric runs with synthetic local files; the external Gradle init script limits execution to one worker/test fork and redirects reports and temporary files to the SSD without removing owner tasks or dependencies.

Manual tests

• Done — no Android device/emulator or installed-package extraction is claimed.

The APK-named binary fixtures exercise the copy workflow; they are not installed or executed. The sample ZIP linked in the issue was blocked by Chrome, so this does not claim reproduction with that exact archive.

• Device: macOS ARM64 build host.
• OS: macOS ARM64 build host; no Android device.
• Environment: JDK 17, Android SDK 34, NDK r28c; managed Rust 1.95 with the configured Android targets.

Build tasks success

• ./gradlew assembleDebug — F-Droid and Play debug builds passed.
• ./gradlew spotlessCheck — passed again on the final test file.

Assembly passed before the helper-only test extraction; app sources and build inputs are byte-identical afterward. Existing upstream resource/deprecation warnings remain. No full test-suite or physical-device claim is made.

Generative code

• This PR used generative code tools (GenAI, LLMs, etc.).
• Model: Codex assistance; exact runtime model identifier is not exposed.
• Version: Not exposed in this runtime.
• Provider: OpenAI.

Codex assisted implementation, actual test execution and review. Independent AI review is not represented as human validation.