fix cloning of DB connection for sqlite in-memory db

fixes #14131
close #14232

framework/db/Connection.php

@@ -1090,8 +1090,11 @@ class Connection extends Component
 
         $this->_master = false;
         $this->_slave = false;
-        $this->pdo = null;
         $this->_schema = null;
         $this->_transaction = null;
+        if (strncmp($this->dsn, 'sqlite::memory:', 15) !== 0) {
+            // reset PDO connection, unless its sqlite in-memory, which can only have one connection
+            $this->pdo = null;
+        }
     }
 }

tests/framework/db/ConnectionTest.php

@@ -351,7 +351,12 @@ abstract class ConnectionTest extends DatabaseTestCase
         $this->assertNotNull($connection->pdo);
 
         $this->assertNull($conn2->transaction);
-        $this->assertNull($conn2->pdo);
+        if ($this->driverName === 'sqlite') {
+            // in-memory sqlite should not reset PDO
+            $this->assertNotNull($conn2->pdo);
+        } else {
+            $this->assertNull($conn2->pdo);
+        }
 
         $connection->beginTransaction();
 
@@ -359,13 +364,23 @@ abstract class ConnectionTest extends DatabaseTestCase
         $this->assertNotNull($connection->pdo);
 
         $this->assertNull($conn2->transaction);
-        $this->assertNull($conn2->pdo);
+        if ($this->driverName === 'sqlite') {
+            // in-memory sqlite should not reset PDO
+            $this->assertNotNull($conn2->pdo);
+        } else {
+            $this->assertNull($conn2->pdo);
+        }
 
         $conn3 = clone $connection;
 
         $this->assertNotNull($connection->transaction);
         $this->assertNotNull($connection->pdo);
         $this->assertNull($conn3->transaction);
-        $this->assertNull($conn3->pdo);
+        if ($this->driverName === 'sqlite') {
+            // in-memory sqlite should not reset PDO
+            $this->assertNotNull($conn3->pdo);
+        } else {
+            $this->assertNull($conn3->pdo);
+        }
     }
 }