You could just measure the gap from the end of the crank arm to the seat tube on both sides. Or the downtube or both. The frame would be unlikely to be bent in both vertical and horizontal planes but the other measurements would rule it out.
@PhilDAS started
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You could just measure the gap from the end of the crank arm to the seat tube on both sides. Or the downtube or both. The frame would be unlikely to be bent in both vertical and horizontal planes but the other measurements would rule it out.