It can be done with times method:
@Test void "should execute closure twice"() { int i = 0 2.times { i++ } assertThat(i).isEqualTo(2) }
Another method is upto which executes given method from one number to another in inclusive way:
@Test void "should execute closure twice with upto"() { int i = 0 0.upto(1, { i++ }) assertThat(i).isEqualTo(2) }
Under the hood both are implemented as simple for loops. However, in writing 2.times or 0.upto is more friendly way to do that.