Add first set of tests for the message_handler

Covering inference runs and other utility messages.

Change-Id: I95958a9e5902fde2003c870c78e0b0f2e8cd7968
diff --git a/applications/message_handler/CMakeLists.txt b/applications/message_handler/CMakeLists.txt
index 8d4ef54..6928c2d 100644
--- a/applications/message_handler/CMakeLists.txt
+++ b/applications/message_handler/CMakeLists.txt
@@ -32,6 +32,7 @@
 math(EXPR TENSOR_ARENA_SIZE "${MESSAGE_HANDLER_ARENA_SIZE} / ${NUM_ARENAS}")
 
 add_subdirectory(lib)
+add_subdirectory(test)
 
 set(MESSAGE_HANDLER_MODEL_0 "" CACHE STRING "Path to built in model 0")
 set(MESSAGE_HANDLER_MODEL_1 "" CACHE STRING "Path to built in model 1")