private static long sizeOf(Blob blob) throws IOException {
    return blob.writeTo(ByteStreams.nullOutputStream()).getSize();
  }
Gets the size of {@code blob}.

@param blob the {@link Blob}
@return the size (in bytes) of {@code blob}
@throws IOException if an I/O exception occurs
jib-core/src/test/java/com/google/cloud/tools/jib/cache/CacheTest.java