@Override
    public long getFileLength() {
      return 1024 * 1024 * 50 + 1;
    }
Construct a ModificationFile using a file as its storage.

@param filePath the path of the storage file.
iotdb-core/datanode/src/test/java/org/apache/iotdb/db/storageengine/dataregion/compaction/inner/InnerSpaceCompactionSelectorTest.java