Need Help - operation not permitted

[sountharcs]

Hi ,
i tried to understand example/hello. what i did is this :
mkdir Test
./hello Test

In another terminal i run this program :

    fp, err := os.OpenFile("Test/file.txt",os.O_RDONLY,0644)
if err != nil {
    fmt.Println(err)
    os.Exit(0)
}
for {
    line, err := br.ReadString('\n')
    if err != nil {
        fmt.Println(line,err)
        break
    }
    fmt.Println(line)
}
fp.Close()

It works as expected.
then i change the code to :

    fp, err := os.OpenFile("Test/file.txt",os.O_WRONLY,0644)
if err != nil {
    fmt.Println(err)
    os.Exit(0)
}
fp.WriteString("Hi Golang")
fp.Close()

It says open Test/file.txt: operation not permitted.

then i did ls Test. Nothing it shows.
i dont understand whats happening.

[hanwen]

the example does

if flags&fuse.O_ANYWRITE != 0 {
    return nil, fuse.EPERM
}