@Test
  public void test012IsDestroyed() throws Exception {
    String regionName = "testIsDestroyed";
    PartitionedRegion pr = (PartitionedRegion) PartitionedRegionTestHelper
        .createPartitionedRegion(regionName, String.valueOf(200), 0);
    pr.put(1, 1);
    pr.get(1);

    if (pr.isDestroyed()) {
      fail(
          "PartitionedRegionSingleNodeOperationsJUnitTest:testIsDestroyed(): Returns true in isDestroyed method, before the region is destroyed");
    }

    pr.destroyRegion();

    if (!pr.isDestroyed()) {
      fail("PartitionedRegionSingleNodeOperationsJUnitTest:testIsDestroyed(): "
          + "Returns false in isDestroyed method, after the region is destroyed");
    }

    if (logWriter.fineEnabled()) {
      logWriter.fine(
          "PartitionedRegionSingleNodeOperationsJUnitTest - testIsDestroyed() Completed successfully ... ");
    }
  }
This method is used to test the isDestroyed() functionality.
geode-core/src/integrationTest/java/org/apache/geode/internal/cache/PartitionedRegionSingleNodeOperationsJUnitTest.java