LoggingConfiguration setFormat(String format) {
    return addSubstitutionVariable(PROPERTY_FORMAT, StringUtils.defaultIfBlank(format, FORMAT_DEFAULT));
  }
@Test
  public void testSetFormat() {
    assertThat(new LoggingConfiguration(null).setFormat("%d %level")
      .getSubstitutionVariable(LoggingConfiguration.PROPERTY_FORMAT)).isEqualTo("%d %level");
  }