Mocking a function inside protected function in an internal class

There is a unit test required for a specific function[ExecuteSelectQuery] which happens to be as such:

  internal abstract class DataRequestProcessor 
    {
    protected DataView ExecuteSelectQuery(SqlDataSource dataSource)
    {
    //do some stuff
   // need to mock this function
    }
    }
    
    internal class AccountDataRequestProcessor  : DataRequestProcessor 
    {
    
    public InfoClass GetSomeDetail(ApiRequest<object> apiRequest)
    {
    ....
    ExecuteSelectQuery(dataSource);
    .....
    }
    }

I thought of going with Interface but DataRequestProcessor simply says to change protection level. Same with if I try to inherit AccountDataRequestProcessor in test class "inconsistent accessibility base class is less accessible than derived class" . Is there a way to Mock the function[ExecuteSelectQuery] when it is called from unit test of class[GetSomeDetail] ? I am using xunit, with 4.5.2 .net framework , c# 7.3