How exactly is tendonitis/tendinosis diagnosed? just by history and palpation?

Physical exam: Tendinitis can usually be diagnosed during the physical exam alone. X-rays, CT MRI tests are ordered to rule out other pathological conditions.

Bendin' the Tendon?: Yes, by learning the mechanism of injury, then examining the injured area and poking around the tendons and ligaments and also testing for any limited range of motion. It may require a specialist if the injury is really bad. Sometimes an MRI will be done to see the extent of injury (if it looks bad from the outside), but not always. They may immobilize the area for a while to see if it will heal.