Expand description
Assert a command stderr string contains a given containee.
Pseudocode:
(command ⇒ stderr ⇒ string) contains (expr into string)
§Example
use assertables::*;
use std::process::Command;
let mut command = Command::new("bin/printf-stderr");
command.args(["%s", "alfa"]);
let containee = "lf";
assert_command_stderr_string_contains!(command, &containee);