What are the tests for hydrocele?

Scrotal ultrasound. Is essentially the only reliable test for hydrocele. Transillumination can be used, but is not 100% reliable because subject with a hydrocele may also have a testicular tumor which is not necessarily seen on transillumination.
Here... Scrotal ultrasound as needed is the most common test for hydrocele after detailed hx and physicals including light transllumination as deemed necessary.