Give the user some guidance where to add missing enumeration values. (#…

…2639)

suite/cstest/include/test_compare.h

@@ -165,7 +165,7 @@ typedef int32_t tbool;
 				#actual " != " #expected ": %" PRId32 \
 					" != %s%s\n", \
 				actual, expected, \
-				found ? "" : " <== id not found"); \
+				found ? "" : " <== id not found. Consider adding it in test_mapping.h::cs_enum_map."); \
 			return ret_val; \
 		} \
 	}