If I use expired Testogel will it still be effective?

Expired medical products can be less effective or risky due to a change in chemical composition or a decrease in strength. Certain expired medications are at risk of bacterial growth and sub-potent antibiotics can fail to treat infections, leading to more serious illnesses and antibiotic resistance.
Once the expiration date has passed there is no guarantee that the medicine will be safe and effective. If your medicine has expired, do not use it.

Source: FDA