Trigger OnSubmit Without Standard Button

When we submit the form using a standard submit button, onSubmit is triggered and form is submitted. When I use a div and call submit() on its onClick event, the form is submitted but onSubmit is not triggered. Is there any possibility to trigger onSubmit explicitly without using button ??

Code:
<form id="testForm" method="post" action="some_file.php" onSubmit="alert('test')">
<div style="width:100px; height:50px; background-image:url('test_button.jpg');" onClick="document.getElementById('testForm').submit()"></div>
</form>