How to create unit test for SOAPConnection.call and mock SOAPConnection?

Question

Welcome to point out any mistake on my code, as this is my first time using SOAP and unit test.

I have a simple SoapService which create SOAPConnection and send the SOAPMessage

SoapService.java

public SOAPMessage sendSoapRequest(String url, String requestString) throws IOException, SOAPException {

    SOAPConnectionFactory soapConnectionFactory = SOAPConnectionFactory.newInstance();
    SOAPConnection soapConnection= soapConnectionFactory.createConnection();


    SOAPResponse soapResponse = soapConnection.call(getSoapMessage(requestString), url);
    soapConnection.close();

    return soapResponse;
}

and I have unit test class for sendSoapRequest

SOAPServiceTest.java

@SpringBootTest
@RunWith(SpringRunner.class)
public class SoapServiceTest {

    @Autowired
    SoapService soapService;

    @Mock
    SOAPConnection mockSoapConnection;

    private SOAPMessage mockSoapResponse = mock(SOAPMessage.class);

    @Test
    public void testSendSoapMessage() throws IOException, SOAPException{

        when(mockSoapConnection.call(any(SOAPMessage.class), anyString())).thenReturn(mockSoapResponse);

        SOAPMessage soapResponse = soapService.sendSoapRequest("http://test.com/test.asmx", "SampleSoapRequestString...");

        Assert.assertNotNull(soapResponse);
        Assert.assertEquals(soapResponse,mockSoapResponse);
    }
}

Referring the code

when(mockSoapConnection.call(any(SOAPMessage.class),anyString())).thenReturn(mockSoapResponse);

it should return mockSoapResponse but it didn't, it actually trying to send the SOAPMessage to the dummy url "http://test.com/test.asmx" when comes to this line

SOAPResponse soapResponse = soapConnection.call(getSoapMessage(requestString), url);.

So my questions are

1. What is the correct way to have a unit test for 'sendSoapRequest`?
2. Is this the correct way to mock the SOAPConnection and define the behavior using Mockito.when ?
3. Am I missing any setup/configuration on the mock ?

I found a related question but it didn't show the complete setup: Java - Mocking soap call with SOAPMessage request

Appreciate for any comment/idea/guide, because I'm really out of idea to get this work. Thank you.