Simple switching environment for tests. On example of getting a current time.

ClockAndTest.scala

package com.blogspot.mpieciukiewicz.clock

import org.joda.time.{DateTimeZone, DateTime, Instant}

trait Clock {
  def now(): Instant
  def dateNow(): DateTime
}

object Clock {
  private var clockInstance: Clock = SystemClock
  def now() = clockInstance.now()
  def dateNow() = clockInstance.dateNow()

  def changeClock(newClock:Clock)(codeBlock: => Unit) {
    val oldClock = Clock.clockInstance
    clockInstance = newClock
    codeBlock
    clockInstance = oldClock
  }
}

object SystemClock extends Clock {
  def now() = Instant.now()
  def dateNow() = DateTime.now()
}

class FakeClock(fixed: DateTime) extends Clock {
  def now() = fixed.toInstant
  def dateNow() = fixed
}


object Test {

  import Clock.changeClock

  def testedMethod() {
    println(Clock.dateNow())
  }

  def main(args: Array[String]) {
    testedMethod()

    changeClock(new FakeClock(new DateTime(2013, 7, 15, 0, 0, DateTimeZone.UTC))) {

      testedMethod()

        changeClock(new FakeClock(new DateTime(2012, 2, 2, 0, 0, DateTimeZone.UTC))) {
          testedMethod()
        }

      testedMethod()
    }

    testedMethod()
  }

}