Just look at it.
We could, of course, complicate the issue by a discussion of what constitutes
'green' - especially for those of us who are red-green colour blind!
But even they rarely have a problem agreeing the colour of grass. The
point is that the "test" - to all normal intents and purposes - requires
a very simple observation. The others, in contrast, require greater or
lesser experimental effort in order to create opportunities for observations.
They also - to a greater or lesser extent - need more sophisticated interpretation
of any results.