def add_fold_column(fold_test_out, fold_num):
    """Add a column to each df in <fold_test_out> specifying which fold the
    prediction was made in"""
    epochs_to_consider = list(fold_test_out.keys())
    for epochstr in epochs_to_consider:
        fold_test_out[epochstr]['FoldNum'] = 'fold_'+str(fold_num)
    return fold_test_out