I'd concur with the FTE comments, but add an important caveat. Flight test measurement, instrumentation, evaluation and interpretation of data is tremendously rewarding and good fun. I am absolutely convinced that being a half-decent TP also requires an inherent feel for flying, not just an understanding of the numbers.
I've had the pleasure of flying with some absolutely first class TP's, all of whom inspired confidence and consequently allowed me to do my measurement, data recording and assessment work to the best of my ability. None were prima donnas and all of this sub-set were modest and easy to direct, even when I asked them to do things I knew to be challenging.
Unfortunately I've also had the misfortune to fly with a few who could politely be described as "unsuited to the role". I can count two that I've flown with as being positively dangerous, to the point of scaring me sh!tless (those who know me will appreciate that this actually takes a reasonably high level of ineptitude..............).
Am I alone in thinking that an honest appraisal of one's own inherent flying aptitude is a pre-requisite for being a good TP?
I recall an ex-colleague of mine (a non-aviator at that time), with whom I used to play table tennis at lunchtime. His hand/eye coordination was astoundingly good; no matter how much I practised his inherent aptitude always meant that he beat me hollow, although he never practiced at all. He became a helicopter pilot and a damned good one at that. I rather suspect that the two are linked and that no amount of training will turn an unsuited individual into an expert.
I learned a long time ago that my own piloting skills were destined to be right at the very modest end of the scale, so I stick to the science and engineering stuff, which is every bit as much fun!