You can test WSDL URLs using external tools like SoapUI and Postman. 

You can create a new SOAP project in SoapUI and provide a WSDL URL to load WSDL. You will need to provide credentials to access WSDL URL in SoapUI.

Then you can fill values in the sample request XML message and send a message and check for a HTTP ok code. If the ok code starts with 2 then the message was sent successfully.