Can somebody help me with this testmethod for an API REST callout.
Here is my callout it, it works just fine when used from a trigger.

public class My_CalloutClass_Stuff {
   @future(callout=true)
    public static void makeCalloutStuff() {

JSONGenerator jsonObj = JSON.createGenerator(true);
    jsonObj.writeStartObject();
    jsonObj.writeFieldName('devices');
    jsonObj.writeStartArray();
        jsonObj.writeStartObject();
        jsonObj.writeFieldName('deviceIds');
        jsonObj.writeStartArray();
            jsonObj.writeStartObject();
                jsonObj.writeStringField('id', 'blah');
                jsonObj.writeStringField('kind', 'blah');
            jsonObj.writeEndObject();
        jsonObj.writeEndArray();            
        jsonObj.writeEndObject();
    jsonObj.writeEndArray();            
    jsonObj.writeEndObject();
String finalJSON = jsonObj.getAsString();
        
    HttpRequest request = new HttpRequest();
        String endpoint = 'http://putsreq.com/YRoCBRnRvcUJ8SD2Rhq0';
        request.setEndPoint(endpoint);
        request.setBody(jsonObj.getAsString());
        request.setHeader('Content-Type', 'application/json');
        request.setMethod('POST');
        String authorizationHeader = 'Bearer ' + 'blah' ;
        String VZHeader = 'blah' ;
        request.setHeader('VZ-M2M-Token', VZHeader);   
        request.setHeader('Authorization', authorizationHeader);    

        // Send the HTTP request and get the response.
        HttpResponse response = new HTTP().send(request);
            System.debug(response.toString());
            System.debug('STATUS:'+response.getStatus());
            System.debug('STATUS_CODE:'+response.getStatusCode());
            System.debug(response.getBody());
           
        // If the request is successful, parse the JSON response.
        if (response.getStatusCode() == 200) {
            // Deserialize the JSON string into collections of primitive data types.
        Map<String, Object> results = (Map<String, Object>) JSON.deserializeUntyped(response.getBody());
            System.debug('=== all keys in the map: ' + results.keySet());
            System.debug('=== all values in the map (as a List): ' + results.values());
            System.debug('=== all values in the map (as a List): ' + results.size());
            
         // Cast the values in the 'blades' key as a list
        List<String> vztoken = new List<String>();
            vztoken.addAll(results.keySet());     

        System.debug('Received the following vztoken info: ' +vztoken);
           for (Object Verizon: vztoken) {
           System.debug(vztoken);
           Verizon__c sbc = new Verizon__c();
           sbc.name=String.valueOf(results.values());
           sbc.vid__c='id';
           sbc.Smartbox__c='id;
           sbc.response_code__c=String.valueOf(results.values());
           sbc.Action__c='Suspend';

           insert sbc;
            
         System.debug('sbc'+sbc);
        }
    }        
}
}


I have a static resource for use with the mocktest

{'sessionresults', 'resultvalue'}



Here is my current, not working testmethod.

@isTest
private class My_CalloutClass_StuffTest {

    @isTest static  void testPUTCallout() {
        // Create the mock response based on a static resource
        StaticResourceCalloutMock mock = new StaticResourceCalloutMock();
        mock.setStaticResource('GetAnimalResource');
        mock.setStatusCode(200);
        mock.setHeader('Content-Type', 'application/json;charset=UTF-8');
        // Associate the callout with a mock response
        Test.setMock(HttpCalloutMock.class, mock);
        // Call method to test
        HttpResponse resA = My_CalloutClass_Stuff.makeCalloutStuff();
        // Verify mock response is not null
        System.assertNotEquals(null,resA,
            'The callout returned a null response.');
        // Verify status code
        System.assertEquals(200,resA.getStatusCode(),
          'The status code is not 200.');
        // Verify content type   
        System.assertEquals('application/json;charset=UTF-8',
          result.getHeader('Content-Type'),
          'The content type value is not expected.');  
        // Verify the array contains 3 items     
        Map<String, Object> results = (Map<String, Object>)
            JSON.deserializeUntyped(resA.getBody());
        List<Object> animals = (List<Object>) results.get('animals');
        System.assertEquals(3, animals.size(),
          'The array should only contain 3 items.');          
    }   

}

Error: Compile Error: Illegal assignment from void to System.HttpResponse at line 13 column 22