tests: Add test for get_mentions()

tests/unittests/test_common.h

@@ -43,3 +43,4 @@ void test_strtoi_range_null_empty_input(void** state);
 void test_strtoi_range_null_err_msg(void** state);
 void test_string_matches_one_of_edge_cases(void** state);
 void test_valid_tls_policy_option(void** state);
+void get_mentions_tests(void** state);