Add regression testing for 'stats_mysql_query_digest' timestamps

- Added regression testing for timestamps 'first_seen' and 'last_seen'.
- Make the test idempotent by cleaning up 'stats_mysql_query_digest'.

test/tap/tests/test_digest_umap_aux-t.cpp

@@ -174,7 +174,7 @@ int main(int argc, char** argv) {
 		return EXIT_FAILURE;
 	}
 
-	plan(1 + DUMMY_QUERIES.size() * 3); // always specify the number of tests that are going to be performed
+	plan(1 + DUMMY_QUERIES.size() * 5); // always specify the number of tests that are going to be performed
 
 	MYSQL *proxy_admin = mysql_init(NULL);
 	if (!mysql_real_connect(proxy_admin, cl.host, cl.admin_username, cl.admin_password, NULL, cl.admin_port, NULL, 0)) {
@@ -199,6 +199,8 @@ int main(int argc, char** argv) {
 		return EXIT_FAILURE;
 	}
 
+	time_t init_time = time(NULL);
+
 	MYSQL_RES *res = NULL;
 	for (const auto &query : DUMMY_QUERIES) {
 		diag("Running: %s", query);
@@ -243,6 +245,8 @@ int main(int argc, char** argv) {
 	);
 
 	vector<digest_stats> ds_vector_after = get_digest_stats(proxy_admin);
+	time_t final_time = time(NULL);
+
 	for (int i = 0; i < DUMMY_QUERIES.size(); i++) {
 		ok(
 			ds_vector_before[i].hostgroup == ds_vector_after[i].hostgroup &&
@@ -285,7 +289,24 @@ int main(int argc, char** argv) {
 			ds_vector_before[i].last_seen, ds_vector_after[i].last_seen,
 			ds_vector_before[i].sum_time, ds_vector_after[i].sum_time
 		);
+
+		uint64_t bf_first_seen = ds_vector_before[i].first_seen;
+		ok(
+			init_time - 1 <= bf_first_seen && init_time + 1 >= bf_first_seen,
+			"'first_seen' within required time range - min: %ld, max: %ld, first_seen: %ld",
+			init_time - 1, init_time + 1, bf_first_seen
+		);
+
+		uint64_t bf_last_seen = ds_vector_before[i].last_seen;
+		ok(
+			init_time <= bf_last_seen && final_time >= bf_last_seen,
+			"'last_seen' within required time range - min: %ld, max: %ld, last_seen: %ld",
+			init_time, final_time, bf_last_seen
+		);
 	}
 
+	mysql_query(proxy_admin, "TRUNCATE TABLE stats.stats_mysql_query_digest");
+	mysql_close(proxy_admin);
+
 	return exit_status();
 }