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 +1,13 @@
+#
+# 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)
+target_sources(app PRIVATE ${app_sources})

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

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+/*
+ * Copyright (c) 2025 Nordic Semiconductor ASA
+ *
+ * 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

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+#
+# 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_UART=y
+CONFIG_ZBUS_MULTIDOMAIN_LOG_LEVEL_DBG=n
+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_TEST_EXTRA_STACK_SIZE=2048
+
+# IPC service support
+CONFIG_EMUL=y
+CONFIG_SERIAL=y
+CONFIG_UART_ASYNC_API=y