public static function create_cache_dir() {
		if ( self::$suite_cache_dir ) {
			self::remove_dir( self::$suite_cache_dir );
		}
		self::$suite_cache_dir = sys_get_temp_dir() . '/' . uniqid( 'wp-cli-test-suite-cache-' . self::$temp_dir_infix . '-', true );
		mkdir( self::$suite_cache_dir );
		return self::$suite_cache_dir;
	}