ExpectedState addSwapSeg(long size, int count) {
      swapMap.put(size, count);
      return this;
    }
Update the swapMap with an entry for a certain file size.
@param size the file size.
@param count the expected number of files
@return {@code this}
ambry-store/src/test/java/com/github/ambry/store/DiskSpaceAllocatorTest.java