tests: zbus: add multidomain proxy agent test suite

Add comprehensive test suite for the zbus multidomain proxy agent
functionality.
Implements a mock backend to enable isolated testing without requiring
actual hardware communication.

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

Author: Trond-F-Christiansen

tests/subsys/zbus/multidomain/proxy_agent/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/zbus_multidomain_mock_backend.c)
+target_sources(app PRIVATE ${app_sources})

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

@@ -0,0 +1,25 @@
+#
+# 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_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
+
+CONFIG_MAIN_STACK_SIZE=2048
+CONFIG_ZBUS_MULTIDOMAIN_PROXY_STACK_SIZE=2048