@Test
public void testLoadAllowedIPAddresses() {

    
    List<IPBlock> ipBlocks = new ArrayList<>();
    InstanceCertManager instance = new InstanceCertManager(null, null, null, true);
    instance.setCertSigner(null);
    // empty or null filename returns success
    assertTrue(instance.loadAllowedIPAddresses(ipBlocks, null));
    assertTrue(instance.loadAllowedIPAddresses(ipBlocks, ""));
    // file does not exist returns failure
    
    assertFalse(instance.loadAllowedIPAddresses(ipBlocks, "some-invalid-filename"));
    // invalid json returns failure
    
    assertFalse(instance.loadAllowedIPAddresses(ipBlocks, "src/test/resources/invalid_ipblocks.txt"));
    
    // valid json with empty set returns failure
    
    assertFalse(instance.loadAllowedIPAddresses(ipBlocks, "src/test/resources/empty_ipblocks.txt"));
    instance.shutdown();
}