I suggest you start by finding out what they are learning English for. improve their promotion chances at work? is the factory going to be bought out and they'll have to speak English at work? or is it just for fun and going on holiday?
When you know why they're learning, you can start planning. As for tests, I supose they just need the usual progress tests to assess how they're doing. The amount of tests will depend on their reasons for learning. If they're learning for fun, they won't need so many tests.
hope this helps