What should you test a heated iron on to ensure it's at the desired temperature?

Testing a heated iron on a piece of tissue paper is effective because tissue paper has a low heat tolerance and will react quickly to temperature changes. When the iron is heated to the desired temperature for styling hair, the tissue paper should not burn or singe upon contact. If it does, that indicates the iron is too hot. This method provides a quick and visible way to assess if the tool is at a safe and effective temperature for hair styling.

The other options, while they might provide some insights, don't serve this particular purpose as effectively. Testing on a small section of hair can be risky, as it may cause damage to the hair if the iron is too hot. A cotton cloth may not burn or react strongly enough to provide a clear indication of the iron's temperature, and a heat-resistant glove, while safe for handling hot tools, won't give a reliable test of the iron's temperature. Using tissue paper stands out as the safest and most immediate way to ensure the iron is ready for use.