Donating a testicle is not a common medical procedure and is generally not practiced. There are several reasons for this:

1. Complexity and Risks: Testicle transplantation involves complex surgery with significant risks, including rejection of the transplanted tissue, complications from surgery, and the need for lifelong immunosuppressive medication for the recipient.

2. Lack of Medical Necessity: Unlike organs such as kidneys, liver, or heart, which are vital for survival, testicles are not essential for life. Their primary functions are the production of sperm and testosterone. Testosterone levels can be managed with hormone replacement therapy, and sperm donation or adoption are alternatives for those dealing with infertility.

3. Ethical and Legal Considerations: There are ethical and legal concerns surrounding the donation and transplantation of reproductive organs. These concerns include issues of consent, the potential for exploitation, and the implications of genetic material being passed on from donor to recipient.

4. Lack of Established Procedures: Unlike kidney or liver transplants, there is no established medical protocol for testicle transplantation. The procedures and long-term outcomes are not well-documented or studied.

In rare cases, testicle transplants have been performed, but these are extremely unusual and typically done in specific circumstances, such as for identical twins where the genetic match reduces the risk of rejection. However, these cases are exceptions and not the norm.