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tests/TC084-lz4-basic.md

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+# Test Case: LZ4 Compression Basic Support
+
+**Test ID**: TC084-lz4-basic  
+
+**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 basic LZ4 compression support for reading compressed files.
+
+## Preconditions
+- EROFS image with LZ4 compression: `test-lz4-basic.erofs`
+- Test file: `/files/test-lz4.txt` (1MB, highly compressible)
+- Mount point: `/mnt/test`
+
+## Test Steps
+1. Mount the LZ4-compressed image:
+   ```
+   mount -t erofs /dev/md0 /mnt/test
+   ```
+
+2. Read entire compressed file:
+   ```
+   cat /mnt/test/files/test-lz4.txt > /tmp/output.txt
+   ```
+
+3. Verify file size:
+   ```
+   stat -f %z /mnt/test/files/test-lz4.txt
+   ```
+
+4. Compare with reference (uncompressed):
+   ```
+   cmp /tmp/output.txt /tmp/reference.txt
+   ```
+
+5. Test multiple LZ4-compressed files:
+   ```
+   for f in /mnt/test/files/lz4-*.txt; do
+     cat "$f" > /dev/null
+   done
+   ```
+
+## Expected Results
+- Step 1: Mount succeeds
+- Step 2: File read successfully, decompressed transparently
+- Step 3: Size matches original uncompressed size (1048576 bytes)
+- Step 4: Files identical (cmp returns 0)
+- Step 5: All LZ4 files read without errors
+
+## Verification Method
+- Verify decompression transparent to application
+- Confirm data integrity after decompression
+- Test LZ4 decompression performance acceptable
+- Verify compressed file sizes smaller than uncompressed
+
+## Cleanup
+```
+umount /mnt/test
+mdconfig -d -u md0
+rm /tmp/output.txt
+```
+
+## Notes
+- LZ4 provides fast decompression with moderate compression ratio
+- EROFS uses LZ4 for general-purpose compression
+- Related tests: TC003 (LZ4 compressed read), TC085 (large files)