php: How to mock a SoapClient response to __soapCall() in a PhpUnit test

I have a service RessortSoapService, which uses the response from a SOAP call.

I inject a class, which gives me the SoapClient back:

public function __construct(ParameterBagInterface $params, SapSoapClientInterface $sapSoapClient)
{
    $this->params = $params;
    $this->soapClient = $sapSoapClient
        ->fetchWdslContent($this->params->get('sapwsdlstruktur'))
        ->getClient();
}

In the SapSoapClient class the method getClient() gives me the properly initialised client back:

public function getClient(): SoapClient
{
    $client = new SoapClient('data://text/plain;base64,' . base64_encode($this->wsdlContent), $this->options);

    return $client;
}

Now I want to write a unittest, which of course should NOT call the Soap server, but just fake a response.

What is did was this:

class RessortSoapServiceTest extends TestCase
{
    public function setUp(): void
    {
        $this->prepareMocks();
        $this->ressortService = new RessortSoapService($this->params, $this->sapSoapClient);
    }

    private function prepareMocks()
    {
....

        $this->soapClient = $this->createMock(SoapClient::class);

        $this->soapClient
            ->method('__soapCall')
            ->willReturnCallback(
            '<SOAP:Envelope xmlns:SOAP="http://schemas.xmlsoap.org/soap/envelope/">
   <SOAP:Header/>
   <SOAP:Body xmlns:urn="urn:sap-com:document:sap:rfc:functions">
      <nm:Z_STA_CUST_GET_RESSORTS.Response xmlns:nm="urn:sap-com:document:sap:rfc:functions" xmlns:prx="urn:sap.com:proxy:PV1:/1SAI/TASC3650D2D2360AAAFB21E:731">
         <ET_RESSORTS>
            <item>
               <GROUP_HIER>0000001</GROUP_HIER>
               <GROUP>0000001</GROUP>
               <IDENT>0000103</IDENT>
               <IS_INACTIVE>0</IS_INACTIVE>
            </item>
... some more XML

         </ET_RESSORTS>
         <ET_RETURN>
            <item>
               <TYPE>S</TYPE>
               <ID>ZSTA</ID>
               <NUMBER>401</NUMBER>
               <MESSAGE>Daten erfolgreich gelesen</MESSAGE>
            </item>
         </ET_RETURN>
      </nm:Z_STA_CUST_GET_RESSORTS.Response>
   </SOAP:Body>
</SOAP:Envelope>'
        );

        $this->sapSoapClient = $this->createMock(SapSoapClientInterface::class);

        $this->sapSoapClient
            ->method('getClient')
            ->willReturnCallback($this->soapClient);
    }

So I created a mock of the native SoapClient, whom I tell, that it should give me back an XML string containing the SOAP XML Response instead of really contacting the SoapServer.

When I run the test __soapCall gives me back null and therefore my test fails.

How can I properly mock my __soapCall response? This is my first use of Soap, so maybe I miss some detail or understanding?

You are using willReturnCallback. This expects a function to be called for the actual response. So it tries to look for a function with the name of your whole xml. Which of course it isn't going to find. If you use willReturn instead, then you should get your desired result.