@Test
  public void testSmallerValue() throws Exception {
    init(UTIL.getConfiguration(), 500);
    byte[] dummyData = makeDummyData(300); // smaller than mob threshold
    Table loader = new RegionAsTable(region);
    // one hfile per row
    for (int i = 0; i < compactionThreshold; i++) {
      Put p = createPut(i, dummyData);
      loader.put(p);
      region.flush(true);
    }
    assertEquals("Before compaction: store files", compactionThreshold, countStoreFiles());
    assertEquals("Before compaction: mob file count", 0, countMobFiles());
    assertEquals("Before compaction: rows", compactionThreshold, UTIL.countRows(region));
    assertEquals("Before compaction: mob rows", 0, countMobRows());

    region.compactStores();

    assertEquals("After compaction: store files", 1, countStoreFiles());
    assertEquals("After compaction: mob file count", 0, countMobFiles());
    assertEquals("After compaction: referenced mob file count", 0, countReferencedMobFiles());
    assertEquals("After compaction: rows", compactionThreshold, UTIL.countRows(region));
    assertEquals("After compaction: mob rows", 0, countMobRows());
  }
During compaction, cells smaller than the threshold won't be affected.
hbase-server/src/test/java/org/apache/hadoop/hbase/mob/TestMobStoreCompaction.java