Mocking a Nested Groovy Method With Mockito

I'm trying to do some testing on a piece of legacy code and I have hit a bit of a wall. The code is part of a backend server for one of our angular web applications. The particular code I need to test is responsible for managing the creation of a sales rep account using data passed in from the client. In addition to saving the new rep to our mongo db, the code also has to handle saving to an external sql db. The work flow looks something like this:

1. Receive 'put' request from client.
2. Create a new 'rep' object with the passed in data.
3. Save the rep to a mongo db.
4. Call a Groovy class that will do an 'insert' on a remote db and return the id of the remote record.
5. Save the remote id into the mongo data.

Normally, I would use Mockito to mock out the sql connection, but I couldn't get that to work for this case. My next thought was to try mocking the Groovy class instead. I don't actually care about the internals of the groovy method, I just need an Id back. So far that has not worked either. The reason I suspect is that the groovy method is getting called from a protected method inside my service class. I don't have any control over the signature of this method, it is an override from another library.

Is there anything I can do to be able to test this code without having to set up an actual connection to the Sql db?

Web Service:

@Override
    protected void beforeInsert() {
        super.beforeInsert();
        final Rep weakRep = this;
        dwPhase1 = injector.getInstance(DwPhase1.class);
        return dwPhase1.insertRepDetail(weakRep);
    }

Mocking code:

DwPhase1 dwGroovy = Mockito.mock(DwPhase1.class);

    Mockito.when(dwGroovy.insertRepDetail(Mockito.any(Rep.class))).then(new Answer<Object>() {

        @Override
        public Object answer(InvocationOnMock invocation) throws Throwable {
            // TODO Auto-generated method stub
            return "hello";
        }
    });

}

Groovy snippet:

  class DwPhase1 extends SQL{
 public Number insertRepDetail(Rep r){
 String insert="""insert into REP_DETAIL (some values)""";
 List<List<Object>> rows =null;
        sql.withTransaction {
            if(update!=null){
                sql.executeUpdate(update);
            }
            rows = sql.executeInsert(params,insert.toString());

        }
        Number dwId =  null;
        if(rows!=null && !rows.isEmpty()){
            List columns=rows.get(0);
            if(columns!=null && !columns.isEmpty()){
                dwId = columns.get(0);
            }
        }
        return dwId;
}
}