CMake: Add MBED_TEST_MODE test application

MBED_TEST_MODE is required for backward compatibilty with CLI1. This
adds a test to ensure that the macro is created when using CLI2 for
testing. This also adds a test in `.travis.yml` that checks whether
CMake defines the macro when BUILD_TESTING is on.

Author: harrisonmutai-arm

.travis.yml

@@ -109,7 +109,15 @@ matrix:
               ':!*tests/*' ':!*targets/*' ':!*TARGET_*' ':!*unsupported/*' \
               ':!*events/tests/*' ':!*drivers/tests/*'
 
-    ### Docs Tests ###
+    - <<: *basic-vm
+      name: "CMake MBED_TEST_MODE check"
+      env: NAME=mbed_test_mode_check
+      script:
+        - mbedtools configure -p tools/cmake/tests/mbed_test_mode -t GCC_ARM -m K64F --mbed-os-path .
+        - cmake -S tools/cmake/tests/mbed_test_mode -B tools/cmake/tests/mbed_test_mode/cmake_build/K64F/develop/GCC_ARM/ -GNinja -DCMAKE_BUILD_TYPE=develop
+        - cmake --build tools/cmake/tests/mbed_test_mode/cmake_build/K64F/develop/GCC_ARM/
+
+        ### Docs Tests ###
     - &docs-vm
       stage: "Docs"
       name: "astyle"

tools/cmake/tests/mbed_test_mode/CMakeLists.txt

@@ -0,0 +1,24 @@
+# Copyright (c) 2020 ARM Limited. All rights reserved.
+# SPDX-License-Identifier: Apache-2.0
+
+cmake_minimum_required(VERSION 3.19.0 FATAL_ERROR)
+
+set(MBED_PATH ${CMAKE_CURRENT_SOURCE_DIR}/../../../.. CACHE INTERNAL "")
+set(MBED_CONFIG_PATH ${CMAKE_CURRENT_BINARY_DIR} CACHE STATIC "")
+
+include(${MBED_PATH}/tools/cmake/app.cmake)
+
+add_executable(mbed-test-mode-check)
+project(mbed-test-mode-check)
+
+set(PROJECT_NAME ${CMAKE_PROJECT_NAME} CACHE INTERNAL "")
+include(CTest)
+
+target_sources(mbed-test-mode-check
+    PRIVATE
+        main.cpp
+)
+
+add_subdirectory(
+    ${MBED_PATH} build
+)

tools/cmake/tests/mbed_test_mode/main.cpp

@@ -0,0 +1,13 @@
+/* mbed Microcontroller Library
+ * Copyright (c) 2021 Arm Limited and Contributors. All rights reserved.
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+#if BUILD_TESTING && !defined(MBED_TEST_MODE)
+#error "MBED_TEST_MODE not defined with BUILD_TESTING on"
+#else
+int main(){
+    return 1;
+}
+#endif