### Question:
Repeater { public Repeater until(Callable<Boolean> exitCondition) { Preconditions.checkNotNull(exitCondition, "exitCondition must not be null"); this.exitCondition = exitCondition; return this; } Repeater();  Repeater(Map<?,?> flags);  Repeater(String description);  Repeater(Map<?,?> flags, String description); void setFromFlags(Map<?,?> flags); static Repeater create(); static Repeater create(Map<?,?> flags); static Repeater create(String description); static Repeater create(Map<?,?> flags, String description); Repeater repeat(); Repeater repeat(Runnable body); Repeater repeat(Callable<?> body); Repeater every(long period, TimeUnit unit); Repeater every(Duration duration); Repeater every(groovy.time.Duration duration); Repeater every(long duration); Repeater until(Callable<Boolean> exitCondition); Repeater rethrowException(); Repeater rethrowExceptionImmediately(); Repeater suppressWarnings(); Repeater limitIterationsTo(int iterationLimit); Repeater limitTimeTo(long deadline, TimeUnit unit); Repeater limitTimeTo(Duration duration); boolean run();  }### Answer:
@Test(expectedExceptions = NullPointerException.class) public void untilFailsIfClosureIsNull() { new Repeater("untilFailsIfClosureIsNull").until(null); }
@Test public void untilSucceedsIfClosureIsNonNull() { new Repeater("untilSucceedsIfClosureIsNonNull").until(Callables.returning(true)); }