public QuotaCounts subtract(QuotaCounts that) {
    nsSsCounts = modify(nsSsCounts, ec -> ec.subtract(that.nsSsCounts));
    tsCounts = modify(tsCounts, ec -> ec.subtract(that.tsCounts));
    return this;
  }
@Test
  public void testSubtract() throws Exception {
    QuotaCounts qc1 = new QuotaCounts.Builder().build();
    QuotaCounts qc2 = new QuotaCounts.Builder().nameSpace(1).storageSpace(512)
        .typeSpaces(5).build();
    qc1.subtract(qc2);
    assertEquals(-1, qc1.getNameSpace());
    assertEquals(-512, qc1.getStorageSpace());
    for (StorageType type : StorageType.values()) {
      assertEquals(-5, qc1.getTypeSpace(type));
    }
  }