Add method to check email priority. Fixes #7.

Author: ssfinney

src/MailTracking.php

@@ -181,6 +181,25 @@ protected function seeEmailFrom($sender, Swift_Message $message = null)
         $this->assertArrayHasKey($sender, (array)$this->getEmail($message)
                                                       ->getFrom(), "The last email sent was not sent from $sender.");
 
+        return $this;
+	 }
+
+    /**
+     * Assert that the last email had the given priority level.
+     * The value is an integer where 1 is the highest priority and 5 is the lowest.
+     *
+     * @param integer            $priority
+     * @param Swift_Message|null $message
+     *
+     * @return PHPUnit_Framework_TestCase $this
+     */
+    protected function seeEmailPriorityEquals($priority, Swift_Message $message = null)
+    {
+        $actual_priority = $this->getEmail($message)
+                                ->getPriority();
+
+        $this->assertEquals($priority, $actual_priority, "The last email sent had a priority of $actual_priority but expected $priority.");
+
         return $this;
     }