I need simulate an exception for a test

Question

I have a problem making a testclass.

I need to simulate an exception for this class:

public class ScheduleOmniAlta50 implements Queueable, Database.AllowsCallouts {

    private String body;

    private String division;

    private static Integer maxRetries = 2;

    private static Integer retryIntervalMinutes = 1;

    public ScheduleOmniAlta50(String body, String division) {

        this.body = body;

        this.division = division;

    }

    public void execute(QueueableContext context) {

        try {

            WSSem.Alta50Response resp = WSSem.sendAlta50(body, division);

        } catch (Exception e) {

            if (AsyncInfo.getCurrentQueueableStackDepth() < maxRetries) {

                ScheduleOmniAlta50 sc = new ScheduleOmniAlta50(body, division);

                ID jobID = System.enqueueJob(sc, retryIntervalMinutes);

            }

        }

    }

}

My test is not going to the catch

@isTest
public class ScheduleOmniAlta50Test implements Database.AllowsCallouts{

    static XHttpCalloutMock getAlta50ResponseError;

    static {

            getAlta50ResponseError  = new XHttpCalloutMock();

            getAlta50ResponseError.buildResponse()

                .withStatus('OK')

                .withStatusCode(200)

                .withBody(SemAuthMock.getTokenResponse())

                .addForAddress(SemAuth.SERVICE_CONFIG.URL__c + '/api/token');

            getAlta50ResponseError.buildResponse()

            .withStatus('ERROR')

            .withStatusCode(404)

            .withBody('{"error": "Error en la solicitud", "hasError" : true}')

            .addForAddress(

                WSSem.SERVICE_CONFIG.URL__c + '/api/Validations/FinalStage'

            );

    }

    @isTest

    static void testExecute_CalloutExceptionThrown() {

        Test.setMock(HttpCalloutMock.class, getAlta50ResponseError);

        ScheduleOmniAlta50 scheduleJob = new ScheduleOmniAlta50('Datos de prueba', 'División de prueba');

        Test.startTest();

        scheduleJob.execute(null);

        Test.stopTest();

        List<AsyncApexJob> retryJobs = [SELECT Id, Status FROM AsyncApexJob];

        System.assertNotEquals(0, retryJobs.size(), 'Debería haber al menos un reintento programado');

    }

}

Thanks.