test code v1

tests/TC003-lz4-compressed-read.md

@@ -0,0 +1,87 @@
+# Test Case: LZ4 Compressed File Read
+
+**Test ID**: TC003-lz4-compressed-read  
+
+**G5 fixture contract**: Use [G5-MANUAL-SETUP.md](G5-MANUAL-SETUP.md).
+Its generated paths, source comparisons, structured corruption offsets, and
+cleanup rules supersede placeholder examples in this file.
+**Category**: Compression  
+**Priority**: Critical  
+**Regression**: None
+
+## Objective
+Verify correct decompression and reading of LZ4-compressed files.
+
+## Preconditions
+- EROFS image with LZ4-compressed files: `test-lz4.erofs`
+- Known reference file: `original.txt` (uncompressed source)
+- Compressed file in image: `/compressed/test.txt`
+- Mount point: `/mnt/test`
+
+## Test Steps
+1. Mount the LZ4 test image:
+   ```
+   mount -t erofs /dev/md0 /mnt/test
+   ```
+
+2. Verify file exists:
+   ```
+   ls -lh /mnt/test/compressed/test.txt
+   ```
+
+3. Read the entire file:
+   ```
+   cat /mnt/test/compressed/test.txt > /tmp/decompressed.txt
+   ```
+
+4. Calculate checksum:
+   ```
+   sha256 /tmp/decompressed.txt
+   sha256 original.txt
+   ```
+
+5. Compare byte-for-byte:
+   ```
+   cmp /tmp/decompressed.txt original.txt
+   ```
+
+6. Test partial read:
+   ```
+   dd if=/mnt/test/compressed/test.txt of=/tmp/partial.txt bs=1024 count=1
+   ```
+
+7. Verify partial read matches:
+   ```
+   cmp -n 1024 /tmp/partial.txt original.txt
+   ```
+
+## Expected Results
+- Step 1: Mount succeeds
+- Step 2: File size matches original uncompressed size
+- Step 4: SHA256 checksums are identical
+- Step 5: `cmp` returns 0 (files identical)
+- Step 7: First 1024 bytes match
+
+## Verification Method
+- Exact byte-for-byte match with original file
+- No corruption in decompressed data
+- File attributes (size, timestamps) preserved correctly
+- Check inode compression format:
+  ```
+  # Using custom debug tool if available
+  erofs_inspect /dev/md0 /compressed/test.txt
+  # Should show: z_algorithmformat[0:2] = Z_EROFS_COMPRESSION_LZ4
+  ```
+
+## Cleanup
+```
+umount /mnt/test
+mdconfig -d -u md0
+rm /tmp/decompressed.txt /tmp/partial.txt
+```
+
+## Notes
+- LZ4 is the most common compression algorithm in EROFS
+- Test should cover files of various sizes: small (<4KB), medium (4KB-1MB), large (>1MB)
+- LZ4 pcluster size is typically 4KB or 64KB
+- Related: TC004 (ztailpacking), TC005 (pcluster mapping)