I think the best test for whether or not something is real is logical consistency.
I have expectations about myself and the world around me when I wake up in the morning that are very similar to what I expected and experienced the day before. I can do this because I have observed and experienced these same set of consistent things on a daily basis from the day I was born. Similarly, people around me expect and experience things in much the same way as I do, allowing us to come to collective agreements about things. For example, we all know and agree on what grass is. We all know and agree on what trees are. We all know and agree that they are mostly green... These consistent and shared experiences are what allow things like language to exist, etc.
This constant logical consistency is what we bank on for determining what is real and what isn't. Dreams, coincidentally, are inconsistent and often illogical - so we recognize what happens in our dream worlds as not being real or tangible, but are projections and illusions of our minds. This is very different from the independent world that surrounds us on a daily basis.