test code v1

tests/TC025-nlink1-handling.md

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+# Test Case: Compact Inode Link-Count Rules
+
+**Test ID**: TC025-nlink1-handling
+
+## Objective
+
+Compare explicit compact link counts, bit-4 single-link encoding, hard links,
+and directory link counts without conflating directory dot omission.
+
+## Fixture
+
+Use `images/compact.erofs` and `images/compact-nlink1.erofs`. Evidence asserts
+explicit `single.txt i_nb=1`, patched bit 4 plus `i_nb=0x1234`, identical
+hard-link NID with `i_nb=2`, and explicit directory nlink.
+
+## Procedure
+
+Mount each image separately and record:
+
+```sh
+stat -f '%N ino=%i nlink=%l mode=%p' \
+  "$mnt/single.txt" "$mnt/hard-a.txt" "$mnt/hard-b.txt" "$mnt/dotdir"
+cmp /tmp/repo22-g1/source/compact/single.txt "$mnt/single.txt"
+cmp /tmp/repo22-g1/source/compact/hard-a.txt "$mnt/hard-a.txt"
+cmp "$mnt/hard-a.txt" "$mnt/hard-b.txt"
+```
+
+Unmount and detach before attaching the second image.
+
+## Expected Results
+
+- Baseline and patched `single.txt` both report nlink 1 for different valid
+  encodings.
+- `hard-a.txt` and `hard-b.txt` share one inode and report nlink 2.
+- `dotdir` uses its explicit directory link count; all data compares pass.