That seems like way more work than what it is worth just to determine if the rim is bent. If you rebuild the wheel entirely, you should use new spokes and a new rim. If the rim is usable, you don't need to replace all the spokes.
If you can true the wheel by adjusting the spokes, the rim is not bent. If the rim is bent you won't be able to true the wheel. Think about it: if the rim is bent to the right, the right side spoke will be loose, and tightening them will only make the problem worse. If that's what you have, you need to remove the spoke closest to the problem, bend the rim back to where it belongs or further, and replace that spoke. OTOH I think sometimes spokes are stressed near their yield points, and stretch under riding loads, letting the wheels go out of true. I've had some success stabilizing a wheel that was always going out of true just by replacing just one spoke. Or maybe the rim is cracked at the spoke hole and that is what is destabilizing the wheel. A wheel can fail in a lot of ways, so you need to examine it carefully if you want to salvage it.

em