tests/drivers/spi/spi_loopback/overlay-cs-loopback-gpio.overlay

#include <zephyr/dt-bindings/gpio/gpio.h>
#include <zephyr/dt-bindings/gpio/arduino-header-r3.h>

/ {
	zephyr,user {
		/* Connect your SPI CS pin to the D8 pin to run the test */
		cs-loopback-gpios = <&arduino_header>,
				    <ARDUINO_HEADER_R3_D8>,
				    <(GPIO_ACTIVE_LOW | GPIO_PUSH_PULL | GPIO_PULL_UP)>;
	};
};