tests: add corejson package test application

tests/pkg_corejson/Makefile

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+include ../Makefile.tests_common
+
+# required packages
+USEPKG += corejson
+
+include $(RIOTBASE)/Makefile.include

tests/pkg_corejson/main.c

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+/*
+ * Copyright (C) 2021 Inria
+ *
+ * This file is subject to the terms and conditions of the GNU Lesser
+ * General Public License v2.1. See the file LICENSE in the top level
+ * directory for more details.
+ */
+
+/**
+ * @ingroup     tests
+ * @{
+ *
+ * @file
+ * @brief       coreJSON package test application
+ *
+ *  Adapted to RIOT style from the [reference example](https://github.com/FreeRTOS/coreJSON#reference-example)
+ *
+ * @author      Alexandre Abadie <alexandre.abadie@inria.fr>
+ *
+ * @}
+ */
+
+#include <stdio.h>
+#include "core_json.h"
+
+int main(void)
+{
+    /* Variables used in this example. */
+    JSONStatus_t result;
+    char buffer[] = "{\"foo\":\"abc\",\"bar\":{\"foo\":\"xyz\"}}";
+    size_t bufferLength = sizeof(buffer) - 1;
+    char queryKey[] = "bar.foo";
+    size_t queryKeyLength = sizeof(queryKey) - 1;
+    char *value;
+    size_t valueLength;
+
+    /* Calling JSON_Validate() is not necessary if the document is guaranteed to be valid. */
+    result = JSON_Validate(buffer, bufferLength);
+
+    if (result == JSONSuccess) {
+        result = JSON_Search(
+            buffer, bufferLength, queryKey, queryKeyLength,
+            &value, &valueLength
+        );
+    }
+
+    if (result == JSONSuccess) {
+        /* The pointer "value" will point to a location in the "buffer". */
+        char save = value[valueLength];
+        /* After saving the character, set it to a null byte for printing. */
+        value[valueLength] = '\0';
+        /* "Found: bar.foo -> xyz" will be printed. */
+        printf("Found: %s -> %s\n", queryKey, value);
+        /* Restore the original character. */
+        value[valueLength] = save;
+    }
+
+    return 0;
+}

tests/pkg_corejson/tests/01-run.py

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+#!/usr/bin/env python3
+
+# Copyright (C) 2021 Inria
+#
+# This file is subject to the terms and conditions of the GNU Lesser
+# General Public License v2.1. See the file LICENSE in the top level
+# directory for more details.
+
+import sys
+from testrunner import run
+
+
+def testfunc(child):
+    child.expect_exact("Found: bar.foo -> xyz")
+
+
+if __name__ == "__main__":
+    sys.exit(run(testfunc))