I’m not sure whether it’s what’s you’re asking or not, but I’d say you may be missing the reshaping of your one testing image.
There shouldn’t be any difference between training with 32 elements in your batch and testing one image.
That’s it (if I’m guessing your dimensions correctly):

Training: 32 x num_channels x width x height

Testing: 1 x num_channels x width x height


Hope it helps