added test case for pgsql transaction module

tests/TransactionPgsqlTestCase.php

+<?php
+class Doctrine_Transaction_Pgsql_TestCase extends Doctrine_Driver_UnitTestCase {
+    public function __construct() {
+        parent::__construct('pgsql');
+    }
+    public function testCreateSavePointExecutesSql() {
+        $this->transaction->createSavePoint('mypoint');
+        
+        $this->assertEqual($this->adapter->pop(), 'SAVEPOINT mypoint');
+    }
+    public function testReleaseSavePointExecutesSql() {
+        $this->transaction->releaseSavePoint('mypoint');
+
+        $this->assertEqual($this->adapter->pop(), 'RELEASE SAVEPOINT mypoint');
+    }
+    public function testRollbackSavePointExecutesSql() {
+        $this->transaction->rollbackSavePoint('mypoint');
+
+        $this->assertEqual($this->adapter->pop(), 'ROLLBACK TO SAVEPOINT mypoint');
+    }
+    public function testSetIsolationThrowsExceptionOnUnknownIsolationMode() {
+        try {
+            $this->transaction->setIsolation('unknown');
+            $this->fail();
+        } catch(Doctrine_Transaction_Exception $e) {
+            $this->pass();
+        }
+    }
+    public function testSetIsolationExecutesSql() {
+        $this->transaction->setIsolation('READ UNCOMMITTED');
+
+        $this->assertEqual($this->adapter->pop(), 'SET SESSION CHARACTERISTICS AS TRANSACTION ISOLATION LEVEL READ UNCOMMITTED');
+    }
+}