I have a two-dimensional uniform `data`. 
I have splitted the `data` on two parts with a `threshold`. 
 
[![enter image description here][1]][1]

    set.seed(20181116) # set the initial seed for generator
    n <- 10000 
    
    data <- data.frame(x=runif(n), y=runif(n))
    
    threshold  <- 0.5      
    plot(data, col=ifelse(data$x > threshold/2 & 
                          data$x < 3*threshold/2 & 
                          data$y < threshold, "red", "black"))

**Question.** What a statistical tests do I use to show that `black` and `red` observations come from a two-dimensional uniform distribution too?

  [1]: https://i.sstatic.net/kzMWv.jpg