Better than a/b testing: http://stevehanov.ca/blog/index.php?id=132

pickByPercentage

import java.util.Random  
Random rand = new Random() 

def colours = ['blue', 'green', 'red', 'yellow']
def likihood = [blue: 25, green: 22, red: 22, yellow: 5]
def views = [blue: 1, green: 1, red: 1, yellow: 1]
def clicks = [blue: 1, green: 1, red: 1, yellow: 1]
def percentages
 
for (def i = 0; i < 10000; i++) {
    def colour

    if (rand.nextInt(100) < 10) {
        colour = colours[rand.nextInt(colours.size())]
    } else {
        percentages = colours.collectEntries {
            [(it): clicks[it]/views[it]*100]
        }
        percentages = percentages.sort {a, b -> b.value <=> a.value}
        colour = percentages.find {true}.key
    }
    
    views[colour] = views[colour] + 1
    
    if (rand.nextInt(100) < likihood[colour]) {
        clicks[colour] = clicks[colour] + 1
    }
}

println clicks.sort {a, b -> b.value <=> a.value}.find{true}
println percentages
println views