zmk/app/tests/to-layer/behavior_keymap.dtsi

#include <dt-bindings/zmk/keys.h>
#include <behaviors.dtsi>
#include <dt-bindings/zmk/kscan_mock.h>

/ {
    keymap {
        compatible = "zmk,keymap";

        default_layer {
            bindings = <
                &to 0  &to 1
                &kp A &kp S>;
        };

        second_layer {
            bindings = <
                &to 0 &to 1
                &kp J  &kp K>;
        };
    };
};