protected HStoreFile createMockStoreFile(final long sizeInBytes, final long seqId) {
    HStoreFile mockSf = mock(HStoreFile.class);
    StoreFileReader reader = mock(StoreFileReader.class);
    String stringPath = "/hbase/testTable/regionA/" + RandomStringUtils.random(FILENAME_LENGTH, 0,
      0, true, true, null, ThreadLocalRandom.current());
    Path path = new Path(stringPath);

    when(reader.getSequenceID()).thenReturn(seqId);
    when(reader.getTotalUncompressedBytes()).thenReturn(sizeInBytes);
    when(reader.length()).thenReturn(sizeInBytes);

    when(mockSf.getPath()).thenReturn(path);
    when(mockSf.excludeFromMinorCompaction()).thenReturn(false);
    when(mockSf.isReference()).thenReturn(false); // TODO come back to
    // this when selection takes this into account
    when(mockSf.getReader()).thenReturn(reader);
    String toString = MoreObjects.toStringHelper("MockStoreFile").add("isReference", false)
      .add("fileSize", Strings.humanReadableInt(sizeInBytes)).add("seqId", seqId)
      .add("path", stringPath).toString();
    when(mockSf.toString()).thenReturn(toString);

    return mockSf;
  }
How many chars long the store file name will be.
hbase-server/src/test/java/org/apache/hadoop/hbase/regionserver/compactions/MockStoreFileGenerator.java