AsyncProcess.cs

static Task RunProcess(ProcessStartInfo psi)
{
    var tcs = new TaskCompletionSource<bool>();
    var process = new Process
    {
        StartInfo = psi,
        EnableRaisingEvents = true
    };
    process.ErrorDataReceived += (s, e) => tcs.SetException(new Exception("err"));
    process.Exited += (sender, args) => tcs.SetResult(true);
    process.Start();
    return tcs.Task;
}