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use futures::executor::block_on;
use futures::io::AsyncReadExt;
#[test]
fn read_exact() {
let mut reader: &[u8] = &[1, 2, 3, 4, 5];
let mut out = [0u8; 3];
let res = block_on(reader.read_exact(&mut out)); // read 3 bytes out
assert!(res.is_ok());
assert_eq!(out, [1, 2, 3]);
assert_eq!(reader.len(), 2);
let res = block_on(reader.read_exact(&mut out)); // read another 3 bytes, but only 2 bytes left
assert!(res.is_err());
assert_eq!(reader.len(), 0);
}