查看的文档，
Response.Body以了解何时从中读取可能返回错误：
// Body represents the response body.//// The response body is streamed on demand as the Body field// is read. If the network connection fails or the server// terminates the response, Body.Read calls return an error.//// The http Client and Transport guarantee that Body is always// non-nil, even on responses without a body or responses with// a zero-length body. It is the caller's responsibility to// close Body. The default HTTP client's Transport may not// reuse HTTP/1.x "keep-alive" TCP connections if the Body is// not read to completion and closed.//// The Body is automatically dechunked if the server replied// with a "chunked" Transfer-Encoding.Body io.ReadCloser
最简单的方法是从测试处理程序生成无效的HTTP响应。
怎么做？有很多方法，一种简单的方法是“撒谎”内容的长度：
handler := func(w http.ResponseWriter, r *http.Request) { w.Header().Set("Content-Length", "1")}该处理程序告诉它具有1个字节的正文，但实际上不发送任何内容。因此，在另一端（客户端）尝试从中读取1个字节时，显然不会成功，并且会导致以下错误：
Unable to read from body unexpected EOF
如果您需要模拟从请求正文（而不是从响应正文）读取错误
