Unfortunately, neuroscience is not at a level where we can actually perform these tests. There is no objective measure to see if someone is in pain, or depressed, or suffering many other psychological symptoms.
Similarly, brain imaging for pain is at the research level, and may come with several other risks. I doubt there are such tests that could be used to conclusively prove that someone is or is not in pain.
There are blood and urine tests for seratonin, but studies are mixed on how reliable they are. Since depression can also be accompanied by other factors though, there is a wide range of tests that can help provide objective evidence.