I think this is what russia is doing with Ukraine now too.

That's not why we are in Ukraine, but I think it's part of the reason why we're in Syria. In Syria, new Russian weapons definitely are getting tested in practice. In Crimea, there wasn't even any fighting, while in the East the separatists (vast majority of them, at least) are not Russian military and they raided the stockpiles of old weapons (think AK-47) formerly owned by Ukrainian military.

We're in Ukraine because in 2014 their government was overthrown and rapidly changed the geopolitical orientation from being pro-Russian (under Viktor Yanukovich) to being pro-American (under Petro Poroshenko and the people around him). People in Crimea and the East of Ukraine, which supported Yanukovich government, didn't like the change all that much.