There are already tests available to
test your monoamines (serotonin, norepinephrine, dopamine). Those are usually
urine tests and they are pretty expansive (about 400-600$ but genetics is an information technology which means it is evolving exponentially which means you will see the price lowered in the years to come) .
Depression can be more complicated than modifications in your monoamines. Some have the biological depression and some don't.