test code v1

tests/TC030-flat-plain-large.md

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+# Test Case: FLAT_PLAIN Large File
+
+**Test ID**: TC030-flat-plain-large
+
+## Objective
+
+Verify a greater-than-10-MiB contiguous `FLAT_PLAIN` file across thousands of
+filesystem blocks.
+
+## Fixture
+
+Use `images/flat.erofs` and `source/flat/large.bin`. Evidence asserts layout 0
+and size 10485791.
+
+## Procedure
+
+```sh
+stat -f 'size=%z blocks=%b' "$mnt/large.bin"
+dd if="$mnt/large.bin" of=/tmp/tc030-full bs=1m
+cmp /tmp/repo22-g1/source/flat/large.bin /tmp/tc030-full
+sha256 /tmp/repo22-g1/source/flat/large.bin /tmp/tc030-full
+./read_probe pread "$mnt/large.bin" 5242880 1048576 /tmp/tc030-seek
+dd if=/tmp/repo22-g1/source/flat/large.bin of=/tmp/tc030-source-seek \
+  bs=1m skip=5 count=1
+cmp /tmp/tc030-source-seek /tmp/tc030-seek
+```
+
+Remove all outputs, unmount, and detach.
+
+## Expected Results
+
+- Reported size is exact; full and seeked data match the source.
+- No mapping error, panic, or cleanup failure occurs.