Function run_with 

pub fn run_with<R, W1, W2>(
    args: &[String],
    stdin: &mut R,
    stdout: &mut W1,
    stderr: &mut W2,
) -> Result<(), RunWithError>
where
    R: BufRead + Read,
    W1: Write,
    W2: Write,

Run the devshell with given args and streams (for tests).

Errors

Returns RunWithError::Usage on invalid args; RunWithError::ReplFailed if the REPL exits with error.