You cannot state with any amount of certainty that OP will have 125mg of exogenous test in his system two weeks after his last pin.
Half lives are not as straight forward as one would think, there are many facets involved. Some components which affect hormone half life include BMI, metabolism, amount of esterase and most importantly injection site. An example of this would be a compound with the acetate ester may have a half life of anywhere from 1-3 days.
Using only the half life formula not very useful for estimating the amount of active hormone. This is because it does not show a true reflection of what is happening inside your body pharmacokinetically. Have a look at the attachment below to see some of the formulas used in determining the pharmakinetics of a compound. That formula sheet doesn't even include taylor or maclaurin series.
Useful Pharmacokinetic Equations