public Map<String, Long> getFreeBytesOnTiers() {
    Map<String, Long> freeCapacityBytes = new HashMap<>();
    for (Map.Entry<String, Long> entry : mUsage.mTotalBytesOnTiers.entrySet()) {
      freeCapacityBytes.put(entry.getKey(),
          entry.getValue() - mUsage.mUsedBytesOnTiers.get(entry.getKey()));
    }
    return freeCapacityBytes;
  }
@Test
  public void getFreeBytesOnTiers() {
    assertEquals(ImmutableMap.of(Constants.MEDIUM_MEM, Constants.KB * 2L,
        Constants.MEDIUM_SSD, Constants.KB * 2L),
        mInfo.getFreeBytesOnTiers());
  }