This is my code:

use std::process::Command;

fn main() {
    let output = Command::new("echo")
    .arg("Hello world")
    .output()
    .expect("Failed to execute command");

    assert_eq!(b"Hello worldn", output.stdout.as_slice());
}

Rust returns this error:

thread 'main' panicked at srcmain.rs:7:6:
Failed to execute command: Error { kind: NotFound, message: "program not found" }      
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
error: process didn't exit successfully: `targetdebugpj_testing.exe` (exit code: 101)

What is wrong?

It is not my first attempt trying this lib. It always returns the same error.