@Test
public void returnsDefaultSeparatorFormattedIndexNameWithoutCustomSeparator() {

    // given
    LogEvent logEvent = mock(LogEvent.class);
    when(logEvent.getTimeMillis()).thenReturn(DEFAULT_TEST_TIME_IN_MILLIS);
    IndexNameFormatter formatter = new RollingIndexNameFormatter(TEST_INDEX_NAME, DATE_PATTERN_WITH_MINUTES, DEFAULT_TEST_TIME_IN_MILLIS, TEST_TIME_ZONE);
    // when
    String formattedIndexName = formatter.format(logEvent);
    // then
    Assert.assertEquals("testIndexName-2017-12-20-23.54", formattedIndexName);
}