private void killSender(EntryEvent event) {
              if (event.isOriginRemote()) {
                Distribution mgr =
                    MembershipManagerHelper.getDistribution(getSystem());
                mgr.requestMemberRemoval(server1ID, "removing for test");
                try {
                  mgr.waitForDeparture(server1ID);
                } catch (Exception e) {
                  fail("failed to stop the other server for this test:" + e.getMessage());
                }
              }
            }
test putIfAbsent with failover & retry. This is bugs 42559 and 43640
geode-core/src/distributedTest/java/org/apache/geode/internal/cache/ConcurrentMapOpsDUnitTest.java