Added a test

Author: SakiTakamachi

ext/pdo_firebird/tests/gh18276.phpt

@@ -0,0 +1,35 @@
+--TEST--
+GH-18276 (persistent connection - setAttribute(Pdo\Firebird::ATTR_DATE_FORMAT, ..) results in "zend_mm_heap corrupted")
+--EXTENSIONS--
+pdo_firebird
+--SKIPIF--
+<?php require('skipif.inc'); ?>
+--XLEAK--
+A bug in firebird causes a memory leak when calling `isc_attach_database()`.
+See https://github.com/FirebirdSQL/firebird/issues/7849
+--FILE--
+<?php
+
+require("testdb.inc");
+unset($dbh);
+
+for ($i = 0; $i < 2; $i++) {
+    $dbh = new PDO(
+        PDO_FIREBIRD_TEST_DSN,
+        PDO_FIREBIRD_TEST_USER,
+        PDO_FIREBIRD_TEST_PASS,
+        [
+            PDO::ATTR_PERSISTENT => true,
+        ],
+    );
+    // Avoid interned
+    $dbh->setAttribute(PDO::FB_ATTR_DATE_FORMAT, str_repeat('Y----m----d', 1));
+    $dbh->setAttribute(PDO::FB_ATTR_TIME_FORMAT, str_repeat('H::::i::::s', 1));
+    $dbh->setAttribute(PDO::FB_ATTR_TIMESTAMP_FORMAT, str_repeat('Y----m----d....H::::i::::s', 1));
+    unset($dbh);
+}
+
+echo 'done!';
+?>
+--EXPECT--
+done!