Will a barium test show all of the stool in the small and large intestines? is it typical to have one performed weeks before the first colonoscopy?

No and no: Barium is a contrast agent which helps the visualization of the bowel during X-ray studies. When given as an enema, it helps for large bowel(colon) examination.Orally, it can help for small bowel evaluation. Neither route is useful for imaging BOTH large and small bowel.If the patient has taken proper bowel preparation measures, there is in fact no stool in the bowel to degrade the visualization.