@Override
        public void append(LogSegment segment, ByteBuffer buffer) throws StoreException {
          int writeSize = buffer.remaining();
          segment.appendFromDirectly(buffer.array(), 0, writeSize);
        }
Tests {@link LogSegment#appendFrom(ByteBuffer)} and {@link LogSegment#appendFrom(ReadableByteChannel, long)} for
various cases.
@throws IOException
ambry-store/src/test/java/com/github/ambry/store/LogSegmentTest.java