public function create_run_dir() {
		if ( !isset( $this->variables['RUN_DIR'] ) ) {
			self::$run_dir = $this->variables['RUN_DIR'] = sys_get_temp_dir() . '/' . uniqid( 'wp-cli-test-run-' . self::$temp_dir_infix . '-', TRUE );
			mkdir( $this->variables['RUN_DIR'] );
		}
	}