Cannot write test for `CLI::prompt()`, `CLI::input()`

[kenjis]

If we write test code for a command that uses CLI::prompt(), and run the test,
it waits for input for ever.

How can we write test?

CodeIgniter4/system/CLI/CLI.php

Line 181 in cf4641c

public static function input(?string $prefix = null): string

[kenjis]

Fixed by #6335