tests: Bluetooth: Increase coverage for sync establishment

We didn't have test coverage for the scenario where the host
starts scanning automatically.

Signed-off-by: Rubin Gerritsen <rubin.gerritsen@nordicsemi.no>

tests/bsim/bluetooth/host/adv/periodic/src/per_adv_syncer.c

@@ -253,6 +253,33 @@ static void main_per_adv_syncer(void)
 	PASS("Periodic advertising syncer passed\n");
 }
 
+static void main_per_adv_syncer_app_not_scanning(void)
+{
+	int err;
+	struct bt_le_per_adv_sync *sync = NULL;
+
+	common_init();
+	start_scan();
+
+	printk("Waiting for periodic advertising...\n");
+	WAIT_FOR_FLAG(flag_per_adv);
+	printk("Found periodic advertising.\n");
+
+	printk("Stopping scan\n");
+	err = bt_le_scan_stop();
+	if (err != 0) {
+		FAIL("Failed to stop scan: %d", err);
+		return;
+	}
+
+	create_pa_sync(&sync);
+
+	printk("Waiting for periodic sync lost...\n");
+	WAIT_FOR_FLAG(flag_per_adv_sync_lost);
+
+	PASS("Periodic advertising syncer passed\n");
+}
+
 static void main_per_adv_conn_syncer(void)
 {
 	struct bt_le_per_adv_sync *sync = NULL;
@@ -341,6 +368,15 @@ static const struct bst_test_instance per_adv_syncer[] = {
 		.test_tick_f = test_tick,
 		.test_main_f = main_per_adv_syncer
 	},
+	{
+		.test_id = "per_adv_syncer_app_not_scanning",
+		.test_descr = "Basic periodic advertising sync test but where "
+			      "the app stopped scanning before creating sync."
+			      "Expect the host to start scanning automatically.",
+		.test_post_init_f = test_init,
+		.test_tick_f = test_tick,
+		.test_main_f = main_per_adv_syncer_app_not_scanning
+	},
 	{
 		.test_id = "per_adv_conn_syncer",
 		.test_descr = "Periodic advertising sync test, but where there "

tests/bsim/bluetooth/host/adv/periodic/tests_scripts/per_adv_app_not_scanning.sh

@@ -0,0 +1,26 @@
+#!/usr/bin/env bash
+# Copyright (c) 2024 Nordic Semiconductor ASA
+# SPDX-License-Identifier: Apache-2.0
+
+# Periodic advertising sync test where the host starts scanning
+# automatically because the application didn't start it.
+
+source ${ZEPHYR_BASE}/tests/bsim/sh_common.source
+
+simulation_id="per_adv_not_scanning"
+verbosity_level=2
+
+cd ${BSIM_OUT_PATH}/bin
+
+Execute ./bs_${BOARD_TS}_tests_bsim_bluetooth_host_adv_periodic_prj_conf \
+  -v=${verbosity_level} -s=${simulation_id} -d=0 -RealEncryption=0 \
+  -testid=per_adv_advertiser -rs=23
+
+Execute ./bs_${BOARD_TS}_tests_bsim_bluetooth_host_adv_periodic_prj_conf \
+  -v=${verbosity_level} -s=${simulation_id} -d=1 -RealEncryption=0 \
+  -testid=per_adv_syncer_app_not_scanning -rs=6
+
+Execute ./bs_2G4_phy_v1 -v=${verbosity_level} -s=${simulation_id} \
+  -D=2 -sim_length=20e6 $@
+
+wait_for_background_jobs