std::io::Read on a [u8]

In a test, I'm trying to pass a fake std::io::Read to some code I'm testing. However, I can't seem to figure out how to use an array or a slice as a Read. I can see there's an impl and the error message indicates that I'm doing something wrong, but I can't see what the problem is. Here's a minimal reproduction of the problem: use std::io::Read; fn do_the_read<R: Read>(r: &mut R) { // Imagine this