Cutting alpha-beta in the well is only an optimization for the basic MiniMax algorithm (i.e. eliminating paths that, of course, would not be accepted by the optimal gaming enemy), so I would simply compare the results of the alpha-beta algorithm with a simpler MiniMax. Once they disagree, you have an error in one of two algorithms.
This simplifies the task of verifying the correctness of your MiniMax algorithm, and I cannot come up with any special tricks for this, but since this is a recursive function, you can write Unittests for all cases
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