@Test
    public void testBasicClose() {
        IdempotentCloser ic = new IdempotentCloser();
        assertFalse(ic.isClosed());
        ic.close();
        assertTrue(ic.isClosed());
    }
Tests basic functionality, i.e. that close <em>means</em> closed.
clients/src/test/java/org/apache/kafka/common/internals/IdempotentCloserTest.java