Add message_handler tests for inference cancellation

Change-Id: Ifdacc47024250e34549d45377795501c371c69f5
diff --git a/applications/message_handler/test/test_assertions.hpp b/applications/message_handler/test/test_assertions.hpp
new file mode 100644
index 0000000..7c4cb5c
--- /dev/null
+++ b/applications/message_handler/test/test_assertions.hpp
@@ -0,0 +1,33 @@
+/*
+ * Copyright (c) 2022 Arm Limited.
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ *
+ * Licensed under the Apache License, Version 2.0 (the License); you may
+ * not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an AS IS BASIS, WITHOUT
+ * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef TEST_ASSERTIONS_H
+#define TEST_ASSERTIONS_H
+
+#include <stddef.h>
+#include <stdio.h>
+
+#define TEST_ASSERT(v)                                                                  \
+    do {                                                                                \
+        if (!(v)) {                                                                     \
+            fprintf(stderr, "%s:%d ERROR test failed: '%s'\n", __FILE__, __LINE__, #v); \
+            exit(1);                                                                    \
+        }                                                                               \
+    } while (0)
+
+#endif