Testosterone can be administered parenterally , but it has more irregular prolonged absorption time and greater activity in muscle in enanthate , undecanoate , or cypionate ester form. These derivatives are hydrolyzed to release free testosterone at the site of injection; absorption rate (and thus injection schedule) varies among different esters, but medical injections are normally done anywhere between semi-weekly to once every 12 weeks. A more frequent schedule may be desirable in order to maintain a more constant level of hormone in the system.  Injectable steroids are typically administered into the muscle, not into the vein, to avoid sudden changes in the amount of the drug in the bloodstream. In addition, because estered testosterone is dissolved in oil, intravenous injection has the potential to cause a dangerous embolism (clot) in the bloodstream.
Taking any form of Steroid if you are diabetic is never a good thing as it makes controlling diabetes B/G levels very much harder due to the inevitable rise in B/G levels. Steroids causes an impact in the body basal metabolism, which makes diabetic patients a susceptible target to that impact increasing or moving the lipid profile and glucose levels to the roof is not regularly control and checked. The short term complications can vary and be very simple(or not) long term complications are a big problem here (macro and micro-vascular complications). Can you use them? maybe… but at the end is your decision. Never do anything without consulting your physician.