I was shipped a USB dongle in a small pink baggie. If it's an anti-static bag I would love to re-use it. How sure can I be that it is, and is there a way to test it?
If you ask the Jet Propulsion Lab (JPL) then 'No'. Pink PP bags have a very thin layer of "ESD" coating that is easy to rub off, and then your left with plastic which isn't good. At a place I worked we could only use them for shipping and then never again.
From Standard: Electrostatic Discharge Control (JPL-D1348_Rev_F)
If you try and test it with a multimeter you may be rubbing the layer off.
2.3.30 Pink-Polyethylene (pink-poly)
The use of pink-poly bags, film, bubble-wrap or foam near any ESDS item or within an ESD protected area is prohibited. Pink-poly provides little protection against ESD events and voltage fields and is a contamination source. The preferred alternative is the metalized static-shielding bag.
Try hooking alligator clips & multimeter leads to the bag.
Good anti-static bags should have some measurable conductivity (i.e. resistance less than infinity/err on your meter).