#[test]
 fn test_zero_observations() {
 let a = Array2::<f32>::zeros((2, 0));
 let pearson = a.pearson_correlation();
 assert_eq!(pearson.shape(), &[2, 2]);
 let all_nan_flag = pearson.iter().map(|x| x.is_nan()).fold(true, |acc, flag| acc & flag);
 assert_eq!(all_nan_flag, true);
 }