Core: uniformRandomSwitch with 6 possibilities sometimes executes nothing

Hi guys,

I think there is a bug in uniformRandomSwitch implementation - when you have i.e. 6 cases defined, sometimes no case is executed at all.

Steps to reproduce:

1. Get fresh gatling-sbt-plugin-demo project (Gatling v3.0.3)
2. Use below simulation:

class ComputerWorld extends Simulation {

  val computerDbScn = scenario("Uniform Random Switch Scenario")
    .forever() {
      exec(_.reset)

        .uniformRandomSwitch(
          exec(_.set("foo", 1)),
          exec(_.set("foo", 2)),
          exec(_.set("foo", 3)),
          exec(_.set("foo", 4)),
          exec(_.set("foo", 5)),
          exec(_.set("foo", 6))
        )

        .doIf("${foo.isUndefined()}") {
          exec(session => {
            println("++++++++++ FOO IS UNDEFINED ++++++++++")
            session
          })
        }
    }

  setUp(
    computerDbScn.inject(atOnceUsers(1))
      .protocols(http.baseUrl("http://computer-database.gatling.io"))
  )
}

1. Execute simulation, i.e. sbt "gatling:testOnly *ComputerWorld"

Actual: There are many executions where variable foo is not defined after executing uniformRandomSwitch.

Expected: uniformRandomSwitch should make sure to always execute one of defined cases.

Cheers, Adam

[slandelle]

@aartajew As I said, I wasn’t satisfied with the existing implementation. New ones looks way better (and has unit tests…).

[aartajew]

I think there is a simpler solution, please see the comment below:

def uniformRandomSwitch(possibilities: ChainBuilder*): B = {
    require(possibilities.size >= 2, "uniformRandomSwitch() requires at least 2 possibilities")

    val possibility1 :: tailPossibilities = possibilities.toList
    val basePercentage = 100d / (tailPossibilities.size + 1) 
    // now round basePercentage to 2 decimals only, the rest is fine
    val firstPercentage = 100d - basePercentage * tailPossibilities.size

    val possibilitiesWithPercentage = (firstPercentage, possibility1) :: tailPossibilities.map((basePercentage, _))

    randomSwitch(possibilitiesWithPercentage, None)
  }