Help writing Salefsorce Api call Test class

Question

I have used some of the guides available like (https://developer.salesforce.com/docs/atlas.en-us.apexcode.meta/apexcode/apex_classes_restful_http_testing_httpcalloutmock.htm), but still having trouble completing the test class. I am not exactly sure how I can call "doAdvancedSearch". This is what I have:

public with sharing class GMSServiceDemo {

    private static String clientId ='4323-4323'; 



    public static List<GMSDonorSearchModel.GMSDonorOutputSearchResult> doAdvancedSearch(GMSDonorSearchModel.GMSDonorInputSearch req){

        List<GMSDonorSearchModel.GMSDonorOutputSearchResult> results = new List<GMSDonorSearchModel.GMSDonorOutputSearchResult>();

        // Get token 
        String token = doLogin();

        // Make the service call
        Http http = new Http();
        HttpRequest request = new HttpRequest();
        request.setTimeout(30000);
        request.setEndpoint('https://myAPI'); 

        request.setMethod('POST');
        request.setHeader( 'Authorization', 'Bearer ' + token );
        request.setHeader('Content-Type', 'application/json');
        request.setHeader('ClientId', clientId);
        request.setBody(JSON.serialize(req));
        System.debug('Request dump: ' + JSON.serialize(req));


        // Make the call
        HttpResponse response = http.send(request);
        System.debug(response);
        if( response.getStatusCode()==200){
            if (!response.getBody().contains('No data found')){ 
                System.debug('Adv Search Response: ' + response.getBody());

                results = (List<GMSDonorSearchModel.GMSDonorOutputSearchResult>)JSON.deserialize(response.getBody(), List<GMSDonorSearchModel.GMSDonorOutputSearchResult>.class);

            } else if (response.getBody().contains('No data found')){
                System.debug('No Data Found: ' + response.getStatusCode() + ': ' + response.getStatus());
              }
        }       
        else {
            System.debug('doAdvanceSearch returned the following status code: ' + response.getStatusCode() + ': ' + response.getStatus());
        }    
        return results;    
    }    
}

This is my MockTest:

@isTest
global class GMSServiceDemoTest implements HttpCalloutMock {

    // Implement this interface method      
    global HTTPResponse respond(HTTPRequest req) {

        System.assertEquals('https:myAPI, req.getEndpoint());
        System.assertEquals('POST', req.getMethod());

        //create fake response
        HttpResponse res = new HttpResponse();
        res.setHeader('Content-Type', 'application/json');
        res.setBody('{"example":"test"}');
        res.setStatusCode(200);
        return res;
    }
}

This is my callout Test:

@isTest
public class GMSCalloutClassTest {

    @isTest 
    static void testCallout(){
      //String  MockAccessToken = 'TestAccessToken';
        //setmock callout class
        Test.setMock(HttpCalloutMock.class, new GMSServiceDemoTest()); 

    }
}