tests: zbus: add multidomain UART backend test suite

Add comprehensive test suite for the zbus multidomain UART backend.
The implementation uses UART emulator devices to enable testing without
requiring physical UART hardware.

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

Author: Trond-F-Christiansen

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

@@ -0,0 +1,8 @@
+# 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)
+target_sources(app PRIVATE ${app_sources})

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

@@ -0,0 +1,22 @@
+/*
+ * Copyright (c) 2023 Meta
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+/ {
+	euart0: uart-emul0 {
+		compatible = "zephyr,uart-emul";
+		status = "okay";
+		current-speed = <0>;
+		rx-fifo-size = <256>;
+		tx-fifo-size = <256>;
+	};
+	euart1: uart-emul1 {
+		compatible = "zephyr,uart-emul";
+		status = "okay";
+		current-speed = <0>;
+		rx-fifo-size = <512>;
+		tx-fifo-size = <512>;
+	};
+};

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

@@ -0,0 +1,28 @@
+CONFIG_ZTEST=y
+CONFIG_ASSERT=n
+CONFIG_LOG=y
+CONFIG_ZBUS=y
+CONFIG_EMUL=y
+CONFIG_ZBUS_CHANNEL_ID=y
+CONFIG_ZBUS_CHANNEL_NAME=y
+CONFIG_ZBUS_MULTIDOMAIN=y
+CONFIG_ZBUS_MULTIDOMAIN_UART=y
+
+CONFIG_UART_ASYNC_API=y
+CONFIG_SERIAL=y
+CONFIG_ZBUS_MULTIDOMAIN_LOG_LEVEL_DBG=n
+
+# Retransmission configuration for faster testing
+CONFIG_ZBUS_MULTIDOMAIN_SENT_MSG_ACK_TIMEOUT=10
+CONFIG_ZBUS_MULTIDOMAIN_SENT_MSG_ACK_TIMEOUT_MAX=100
+CONFIG_ZBUS_MULTIDOMAIN_MAX_TRANSMIT_ATTEMPTS=5
+
+# Increase message pool size for testing multiple scenarios
+CONFIG_ZBUS_MULTIDOMAIN_SENT_MSG_POOL_SIZE=16
+
+# FFF (Fake Function Framework) for mocking
+CONFIG_ZTEST_MOCKING=y
+
+# IPC service support
+CONFIG_IPC_SERVICE=y
+CONFIG_MBOX=y