valid_url rule not working

form validation rule "valid_url" not working as expected. here is my code

PHP Code:

$this->form_validation->set_rules('website', 'Website', 'required|valid_url'); 


this rule returning true for string "test" for following markup

PHP Code:

<input type="text" class="form-control" id="website" name="website" placeholder="Website Address" required/> 


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