If you ask old doctors, they will unanimously say that the younger set of doctors relies way too heavily on getting tests. Your history and exam should tell you the diagnosis, they say; tests are to confirm what you already know is there. Spend more time talking to and examining the patient, and you will find out what is wrong with them easily.
There are many situations where I can do just that. I spent years learning the art of history taking and physical diagnosis, and don't need that many tests. That's why I get so annoyed when parents demand them. I really don't get that irritated when parents just ask if I shouldn't be doing some (unspecified) test. But I do get ticked when parents with no medical training whatsoever (except, I guess, from Google U) think they know just WHAT tests I should be ordering. News flash: that was also part of my training. So was risk-benefit ratio. That CT scan you're demanding won't tell me anything I need to know; and will expose your child to a shocking amount of ionizing radiation that will put him or her at higher risk of cancer down the road. And if it is a belly CT, their reproductive organs will get irradiated. You are putting not only your child, but your future grandchildren, at risk. If I feel that a CT is necessary to care for your child, I certainly will not hesitate to get one. But I don't like to get any testing if I don't have something useful to learn from it. Please, let me do my job.
