@Test
  public void testAccessingClosedDistributedSystem() {
    Properties props = new Properties();

    // a loner is all this test needs
    props.setProperty(MCAST_PORT, "0");
    props.setProperty(LOCATORS, "");
    InternalDistributedSystem system = createSystem(props);
    system.disconnect();

    assertThatThrownBy(system::getDistributionManager)
        .isInstanceOf(DistributedSystemDisconnectedException.class);
    system.getLogWriter();
  }
Tests that getting the log level is what we expect.
geode-core/src/integrationTest/java/org/apache/geode/distributed/internal/InternalDistributedSystemIntegrationTest.java