There is no test you take for depression. There is no medicine you can take and cure you.
There is no such thing as "normal" brain chemistry. We all have different physiology. When you read about studies referring to depression they examine the ones complaining about depression vs the ones who don't. This is a generic problem with medicine. Add to that the fact that if you believe you have a certain disease you start acting like it and science of fMRI goes out of the window.
I did do a lot of reading about it don't worry.
Honestly, that's a very juvenile argument. Most of the mental illnesses don't have a sure shot test or a medicine that cures you 100%. That doesn't make the illness "made up", it just shows how complex the brain and it's chemistry is. Besides, on what basis are you challenging established medical evidence? Besides your seemingly pure contempt for mentally "weak" people, I really don't see you countering anything with any science to back it up.