To test that a sample $X_1,\ldots,X_n$ are i.i.d against that the distributions of $X_i$ are stochastically increasing in $i$, how to find the distribution of the test statistic and the critical value for large $n$?
I suppose that the U-statistic, $U=\frac{1}{n \choose 2}\sum_{i<j}1\{X_j-X_i>0\}$. But how do I find the critical value?