System.InvalidOperationException : Could not find the dialect in the configuration

[Junior Lapuñete]

I try running the NHibernate Unit of Work Example using xunit
[Fact]
     public void SetupContext()
     {
        UnitOfWork.Configuration.AddAssembly(Assembly.GetExecutingAssembly());
        new SchemaExport(UnitOfWork.Configuration).Execute(false, true, false, false);

     }

And this is the error message:

Message:
    System.InvalidOperationException : Could not find the dialect in the configuration
  Stack Trace:
    Dialect.GetDialect(IDictionary`2 props)
    SchemaExport.Initialize()
    SchemaExport.InitConnectionAndExecute(Action`1 scriptAction, Boolean execute, Boolean justDrop, DbConnection connection, TextWriter exportOutput)
    SchemaExport.Execute(Boolean useStdOut, Boolean execute, Boolean justDrop)
    Test_usage_of_UnitOfWork.SetupContext() line 14

Anybody here can help me?

Thanks.