public void start(long period, TimeUnit unit) {
        start(period, period, unit);
    }
@Test(expected = IllegalArgumentException.class)
    public void shouldDisallowToStartReportingMultipleTimesOnCustomExecutor() throws Exception {
        reporterWithCustomExecutor.start(200, TimeUnit.MILLISECONDS);
        reporterWithCustomExecutor.start(200, TimeUnit.MILLISECONDS);
    }