  Out-of-distribution (OOD) testing is increasingly popular for evaluating a
machine learning system's ability to generalize beyond the biases of a training
set. OOD benchmarks are designed to present a different joint distribution of
data and labels between training and test time. VQA-CP has become the standard
OOD benchmark for visual question answering, but we discovered three troubling
practices in its current use. First, most published methods rely on explicit
knowledge of the construction of the OOD splits. They often rely on
``inverting'' the distribution of labels, e.g. answering mostly 'yes' when the
common training answer is 'no'. Second, the OOD test set is used for model
selection. Third, a model's in-domain performance is assessed after retraining
it on in-domain splits (VQA v2) that exhibit a more balanced distribution of
labels. These three practices defeat the objective of evaluating
generalization, and put into question the value of methods specifically
designed for this dataset. We show that embarrassingly-simple methods,
including one that generates answers at random, surpass the state of the art on
some question types. We provide short- and long-term solutions to avoid these
pitfalls and realize the benefits of OOD evaluation.
