This sentence does not work in German, not even as an imperative sentence. Better would be brasil2004's suggestion "Wir werden in ein paar Jahren wieder testen!" (We will test again in a few years) or "Lasst uns in ein paar Jahren wieder testen!" (Let us test again in a few years)
In English, you would say "a few" in this context. "Few" without an article has a slightly different meaning. For example:
"I have a few books." = "I have some books." [an unspecified number, though probably not a huge number]. "I have few books." = "I don't have very many books." (emphasis is on the small quantity).