Testing reality simply means to compare
what your critical voice says is going on to what,
in reality, is actually going on the outside.
A basic example would be to look at a tree.
You may or may not like the tree, but by truthfully observing,
one can easily see that one's critical reaction to the tree is irrelevant.
Your approval or disapproval, like or dislike of the tree,
not only has no bearing on it,
it also blinds your ability to observe its shape, form, location, and context.
This is, as I said, a very basic example, but an actor must realize
that practically all of one's experience of life is distorted
by a slavish adherence to this critical faculty.