func TestLogOutput(t *testing.T) {
    var buf bytes.Buffer
    log.SetOutput(&buf)
    defer log.SetOutput(os.Stderr) // 测试后恢复

    log.Println("hello, world")

    output := buf.String()
    if !strings.Contains(output, "hello, world") {
        t.Errorf("期望日志包含 'hello, world'，实际: %s", output)
    }
}

var logger = log.New(os.Stderr, "", log.LstdFlags)

func doSomething() {
    logger.Println("doing work")
}

func TestCustomLogger(t *testing.T) {
    var buf bytes.Buffer
    logger.SetOutput(&buf)
    defer logger.SetOutput(os.Stderr)

    doSomething()

    output := buf.String()
    if !strings.Contains(output, "doing work") {
        t.Errorf("未捕获预期日志: %s", output)
    }
}

func TestWithMultiWriter(t *testing.T) {
    var buf bytes.Buffer
    multiWriter := io.MultiWriter(&buf, os.Stderr)
    log.SetOutput(multiWriter)
    defer log.SetOutput(os.Stderr)

    log.Print("test message")

    if !strings.Contains(buf.String(), "test message") {
        t.Error("日志未正确写入缓冲区")
    }
}