A test for gluten development: stretch a small piece of dough thin enough to see light through it without tearing.
Pull off a small piece of dough and gently stretch it between your fingers in all directions. If you can stretch it paper-thin with light passing through it before it tears, your gluten is well developed. If it tears before becoming translucent, it needs more kneading or resting time. This test works best for wheat-based doughs -- low-gluten flours like rye will never pass it, and that's fine. It's also useful for testing how much water your flour can handle.
