def METHOD_NAME(self, batch):
    # NB: `batch` is `torch_geometric.data.batch.Batch` type
    output = self.model(batch)
    loss = F.nll_loss(output, batch.y)
    pred = output.max(dim=1)[1]
    accuracy = pred.eq(batch.y).sum().item() / len(batch.y)
    return {
        "accuracy": accuracy,
        "validation_loss": loss,
    }