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.