@Test
  public void testGetDifferentSystem() {
    Properties config = createLonerConfig();
    config.setProperty(MCAST_FLOW_CONTROL, "3000000,0.20,3000");

    DistributedSystem.connect(config);

    config.setProperty(MCAST_ADDRESS, "224.0.0.1");

    assertThatThrownBy(() -> DistributedSystem.connect(config))
        .isInstanceOf(IllegalStateException.class);
  }
Tests that getting a <code>DistributedSystem</code> with a different configuration after one
has already been obtained throws an exception.
geode-core/src/distributedTest/java/org/apache/geode/distributed/DistributedSystemDUnitTest.java