tests: zbus: add multidomain IPC backend test suite

Add comprehensive test suite for the zbus multidomain IPC backend.
The implementation includes a mock IPC backend to enable isolated testing
without requiring actual hardware communication between cores.

Signed-off-by: Trond F. Christiansen <[email protected]>

Author: Trond-F-Christiansen

tests/subsys/zbus/multidomain/ipc_backend/CMakeLists.txt

@@ -0,0 +1,13 @@
+#
+# Copyright (c) 2025 Nordic Semiconductor ASA
+#
+# SPDX-License-Identifier: Apache-2.0
+#
+
+cmake_minimum_required(VERSION 3.20.0)
+
+find_package(Zephyr REQUIRED HINTS $ENV{ZEPHYR_BASE})
+project(test_channel_name)
+
+FILE(GLOB app_sources src/main.c src/mock_ipc.c)
+target_sources(app PRIVATE ${app_sources})

tests/subsys/zbus/multidomain/ipc_backend/app.overlay

@@ -0,0 +1,12 @@
+/*
+ * Copyright (c) 2025 Nordic Semiconductor ASA
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+/ {
+	fake_ipc: fake_ipc_device {
+		compatible = "fake-ipc";
+		status = "okay";
+	};
+};

tests/subsys/zbus/multidomain/ipc_backend/dts/bindings/fake-ipc.yaml

@@ -0,0 +1,3 @@
+description: Fake IPC backend for testing zbus multidomain
+
+compatible: "fake-ipc"

tests/subsys/zbus/multidomain/ipc_backend/prj.conf

@@ -0,0 +1,27 @@
+#
+# Copyright (c) 2025 Nordic Semiconductor ASA
+#
+# SPDX-License-Identifier: Apache-2.0
+#
+
+CONFIG_LOG=y
+CONFIG_CRC=y
+CONFIG_ZBUS=y
+CONFIG_ZBUS_CHANNEL_NAME=y
+CONFIG_ZBUS_MSG_SUBSCRIBER=y
+
+CONFIG_ZBUS_MULTIDOMAIN=y
+CONFIG_ZBUS_MULTIDOMAIN_IPC=y
+CONFIG_ZBUS_MULTIDOMAIN_LOG_LEVEL_INF=y
+CONFIG_ZBUS_MULTIDOMAIN_SENT_MSG_ACK_TIMEOUT=10
+CONFIG_ZBUS_MULTIDOMAIN_SENT_MSG_ACK_TIMEOUT_MAX=100
+CONFIG_ZBUS_MULTIDOMAIN_MAX_TRANSMIT_ATTEMPTS=5
+CONFIG_ZBUS_MULTIDOMAIN_SENT_MSG_POOL_SIZE=16
+
+CONFIG_ZTEST=y
+CONFIG_ASSERT=n
+CONFIG_ZTEST_MOCKING=y
+
+# IPC service support
+CONFIG_IPC_SERVICE=y
+CONFIG_MBOX=y