Following can be the possibilities;
1) Cyst of an appendage of the testes; this can be pedunculated (stem like mushroom) and can undergo torsion or can get inflamed, so it can become tender and/or painful.
3) Cysts of epididymis; called as
a) hydatid of Morgagni (appendix of the epididymis)
b) vas aberrans of Haller
All of these are benign (non cancerous), thus not worrying, but would need attention of your primary care physician for an evaluation and ultrasound to pin point the diagnosis.
I would be happy to assist you further, if you need any more information.
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