test code v1

tests/TC081-metabox-backed-xattr.md

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+# Test Case: Metabox-backed shared xattrs
+
+**Test ID**: TC081-metabox-backed-xattr
+**Fixture**: `metabox-plain.erofs`, `/metabox-a`, `/metabox-b`
+
+## Objective
+
+Verify shared entries, inline entries, and long-prefix shared entries from a
+metabox logical stream. Require `SHARED_EA_IN_METABOX`, `xattr_blkaddr=1`,
+carrier size/bounds, shared IDs, and prefix fields in the generator manifest.
+
+## Manual steps
+
+```sh
+lsextattr user /mnt/repo22-g4/metabox-a
+getextattr -qq -x user metaboxshared /mnt/repo22-g4/metabox-a
+getextattr -qq -x user metaboxshared /mnt/repo22-g4/metabox-b
+getextattr -qq -x user shared-prefix-key /mnt/repo22-g4/metabox-a
+getextattr -qq -x user repo22.application.component.setting \
+  /mnt/repo22-g4/metabox-a
+```
+
+## Expected results
+
+Values are `nonzero-base`, `nonzero-base`, `shared-value`, and
+`long-prefix-value`; all names list once. Clean up.