to save roundtrips use batch selects with ToFutureValue
var sessions = results.Select(cbtAppointmentDto => Session.QueryOver<TestSession>()
.Where(x => x.SessionName == cbtAppointmentDto.ExamSeriesCode)
.FutureValue()).ToOList();
for (int i = 0; i < sessions.Count; i++)
{
var session = sessions[i].Value;
if (session != null)
{
results[i].TestStartDate = session.TestsStartDate;
results[i].TestEndDate = session.TestsEndDate;
}
}