@Test
  public void testExists() {
    CacheTransactionManager mgr = cache.getCacheTransactionManager();
    mgr.begin();
    TransactionId txId = mgr.suspend();
    assertTrue(mgr.exists(txId));
    mgr.resume(txId);
    assertTrue(mgr.exists(txId));
    mgr.commit();
    assertFalse(mgr.exists(txId));

    mgr.begin();
    txId = mgr.suspend();
    assertTrue(mgr.exists(txId));
    mgr.resume(txId);
    assertTrue(mgr.exists(txId));
    mgr.rollback();
    assertFalse(mgr.exists(txId));
  }
two threads suspend and resume a single transaction, while making changes.
geode-core/src/integrationTest/java/org/apache/geode/internal/cache/TXManagerImplJUnitTest.java