When conducting a landing page test, you are probably offering potential customers your product before it’s even built.
You should not disclose that information too early, to be certain that the data you acquire is based on the true purchase intents of potential customers. This removes any bias or reservations they may have if they would be aware they are being tested.
It is only at the end, that you should disclose that the product is not yet available. We'll show you how it's done.