Class generated from WSDL:
//Generated by wsdl2apex


public class ParkService {
    public class byCountryResponse {
        public String[] return_x;
        private String[] return_x_type_info = new String[]{‘return’,’http://parks.services/’,null,’0′,’-1′,’false’};
        private String[] apex_schema_type_info = new String[]{‘http://parks.services/’,’false’,’false’};
        private String[] field_order_type_info = new String[]{‘return_x’};
    }
    public class byCountry {
        public String arg0;
        private String[] arg0_type_info = new String[]{‘arg0′,’http://parks.services/’,null,’0′,’1′,’false’};
        private String[] apex_schema_type_info = new String[]{‘http://parks.services/’,’false’,’false’};
        private String[] field_order_type_info = new String[]{‘arg0’};
    }
    public class ParksImplPort {
        public String endpoint_x = ‘https://th-apex-soap-service.herokuapp.com/service/parks’;
        public Map<String,String> inputHttpHeaders_x;
        public Map<String,String> outputHttpHeaders_x;
        public String clientCertName_x;
        public String clientCert_x;
        public String clientCertPasswd_x;
        public Integer timeout_x;
        private String[] ns_map_type_info = new String[]{‘http://parks.services/’, ‘ParkService’};
        public String[] byCountry(String arg0) {
            ParkService.byCountry request_x = new ParkService.byCountry();
            request_x.arg0 = arg0;
            ParkService.byCountryResponse response_x;
            Map<String, ParkService.byCountryResponse> response_map_x = new Map<String, ParkService.byCountryResponse>();
            response_map_x.put(‘response_x’, response_x);
            WebServiceCallout.invoke(
              this,
              request_x,
              response_map_x,
              new String[]{endpoint_x,
              ”,
              ‘http://parks.services/’,
              ‘byCountry’,
              ‘http://parks.services/’,
              ‘byCountryResponse’,
              ‘ParkService.byCountryResponse’}
            );
            response_x = response_map_x.get(‘response_x’);
            return response_x.return_x;
        }
    }
}


Class making use of WSDL generated Class:
public class ParkLocator {
    public static List < String > country(String Country) {
        ParkService.ParksImplPort obj = 
            new ParkService.ParksImplPort();
        return obj.byCountry(Country);
    }
}


Mock for test class:
@isTest
global class ParkServiceMock implements WebServiceMock {
   global void doInvoke(
           Object stub,
           Object request,
           Map<String, Object> response,
           String endpoint,
           String soapAction,
           String requestName,
           String responseNS,
           String responseName,
           String responseType) {
        ParkService.byCountryResponse response_x = 
            new ParkService.byCountryResponse();
        response_x.return_x = new List < String > {‘a’, ‘b’};
        response.put(‘response_x’, response_x); 
   }
}


Test Class:
@isTest
private class ParkLocatorTest {
    @isTest static void testCallout() {              
        Test.setMock(WebServiceMock.class, new ParkServiceMock());
        List < String > result = ParkLocator.country(‘Test’);
    }
}


Cheers!!!