Question

We’ve come across a very peculiar behaviour with mocks and sets in Spock.

In a Spock (0.5, Groovy 1.7) given: block (amount is an Integer):

Set<Operand> operands=new HashSet<Operand>()
for (index in amount){
  operand = Mock(Operand)
  operand.update() >> null
  operands.add(operand)
}

After each loop run (breakpoint on closing bracket), there’s only one (1) element in the set, when the loop starts anew, operands.size() == 0. Apparently, the mock objects mysteriously disappear.

In the following version, everything works and the set has operands.size() == amount after the loop runs.

Set<Operand> operands=new HashSet<Operand>()
amount.times{
  operand = Mock(Operand)
  operand.update() >> null
  operands.add(operand)
}

Does anyone have an idea why the first version does not work?

Answer 1

The problem is unrelated to Spock (and Sets). for (index in amount) is simply not a correct way to write a loop with amount iterations in Groovy. After in, Groovy expects something that it knows how to iterate over (e.g. an Iterable). The fallback is to (logically) treat an object as a collection containing just itself. This explains why you get just one iteration where index == amount.

The shortest way to write a loop with amount iterations is amount.times {}, as in your second snippet.