} catch (final Exception e) {
            fail("completeOperation should not throw: " + e.getMessage());
        }
    }

    @Test
    public void test_completeOperation_doubleCall_safe() {
        // Calling completeOperation twice must not throw (idempotent release)
        final AtomicInteger callCount = new AtomicInteger(0);
        final CoordinatorHelper helper = new CoordinatorHelper() {