netty(八）--EmbeddedChannel单元测试

最佳实践要求你的测试不仅要能够证明你的实现是正确的，而且容易隔离那些因修改代码而突然出现的问题。这种类型的测试叫做单元测试。
EmbeddedChannel是netty专门改进针对ChannelHandler的单元测试而提供的。
核心方法：

数据流：

---

测试入站消息

测试1是直接写入9个字节，被拆分成3个桢，
测试2是分2次写入，第一次2个字节，第二次7个字节，结果和测试1一样。
finish方法将EmbeddedChannel标记为已完成状态。

public class FixedLengthFrameDecoderTest {
    @Test
    public void testFramesDecoded(){
        ByteBuf buf= Unpooled.buffer();
        for (int i=0;i<9;i++){
            buf.writeByte(i);
        }
        ByteBuf input=buf.duplicate();
        EmbeddedChannel channel=new EmbeddedChannel(
                new FixedLengthFrameDecoder(3)
        );
        assertTrue(channel.writeInbound(input.retain()));
        assertTrue(channel.finish());

        //读取消息
        ByteBuf read=channel.readInbound();
        assertEquals(buf.readSlice(3),read);
        read.release();

        read = (ByteBuf) channel.readInbound();
        assertEquals(buf.readSlice(3), read);
        read.release();
        read = (ByteBuf) channel.readInbound();
        assertEquals(buf.readSlice(3), read);
        read.release();
        assertNull(channel.readInbound());
        buf.release();
    }
    @Test
    public void testFramesDecoded2() {
        ByteBuf buf = Unpooled.buffer();
        for (int i = 0; i < 9; i++) {
            buf.writeByte(i);
        }
        ByteBuf input = buf.duplicate();
        EmbeddedChannel channel = new EmbeddedChannel(
                new FixedLengthFrameDecoder(3));
        assertFalse(channel.writeInbound(input.readBytes(2)));
        assertTrue(channel.writeInbound(input.readBytes(7)));
        assertTrue(channel.finish());
        ByteBuf read = (ByteBuf) channel.readInbound();
        ByteBuf b2=buf.readSlice(3);
        assertEquals(b2, read);
        read.release();
        read = (ByteBuf) channel.readInbound();
        assertEquals(buf.readSlice(3), read);
        read.release();
        read = (ByteBuf) channel.readInbound();
        assertEquals(buf.readSlice(3), read);
        read.release();
        assertNull(channel.readInbound());
        buf.release();
    }

}

解码器：

public class FixedLengthFrameDecoder extends ByteToMessageDecoder {
    private final int frameLength;

    public FixedLengthFrameDecoder(int frameLength) {
        this.frameLength = frameLength;
    }

    @Override
    protected void decode(ChannelHandlerContext channelHandlerContext, ByteBuf byteBuf, List