code: /*
   * Copyright (c) 2022 Airbyte, Inc., all rights reserved.
   */
  
  package io.airbyte.commons.util;
  
  import static org.junit.jupiter.api.Assertions.assertEquals;
  import static org.junit.jupiter.api.Assertions.assertFalse;
  import static org.junit.jupiter.api.Assertions.assertThrows;
  import static org.junit.jupiter.api.Assertions.assertTrue;
  import static org.mockito.Mockito.mock;
  import static org.mockito.Mockito.verify;
  
  import io.airbyte.commons.concurrency.VoidCallable;
  import java.util.Collections;
  import java.util.Iterator;
  import org.junit.jupiter.api.Test;
  
  class DefaultAutoCloseableIteratorTest {
  
    @Test
    void testNullInput() {
      final VoidCallable onClose = mock(VoidCallable.class);
      assertThrows(NullPointerException.class, () -> new DefaultAutoCloseableIterator<>(null, onClose));
      assertThrows(NullPointerException.class, () -> new DefaultAutoCloseableIterator<>(Collections.emptyIterator(), null));
      assertThrows(NullPointerException.class, () -> new DefaultAutoCloseableIterator<>(null, null));
    }
  
    @Test
    void testEmptyInput() throws Exception {
      final VoidCallable onClose = mock(VoidCallable.class);
      final AutoCloseableIterator<String> iterator = new DefaultAutoCloseableIterator<>(Collections.emptyIterator(), onClose);
      assertFalse(iterator.hasNext());
      iterator.close();
      verify(onClose).call();
    }
  
    @Test
    void test() throws Exception {
      final VoidCallable onClose = mock(VoidCallable.class);
      final AutoCloseableIterator<String> iterator = new DefaultAutoCloseableIterator<>(MoreIterators.of("a", "b", "c"), onClose);
  
      assertNext(iterator, "a");
      assertNext(iterator, "b");
      assertNext(iterator, "c");
      iterator.close();
  
      verify(onClose).call();
    }
  
    @Test
    void testCannotOperateAfterClosing() throws Exception {
      final VoidCallable onClose = mock(VoidCallable.class);
      final AutoCloseableIterator<String> iterator = new DefaultAutoCloseableIterator<>(MoreIterators.of("a", "b", "c"), onClose);
  
      assertNext(iterator, "a");
      assertNext(iterator, "b");
      iterator.close();
      assertThrows(IllegalStateException.class, iterator::hasNext);
      assertThrows(IllegalStateException.class, iterator::next);
      iterator.close(); // still allowed to close again.
    }
  
    private void assertNext(final Iterator<String> iterator, final String value) {
      assertTrue(iterator.hasNext());
      assertEquals(value, iterator.next());
    }
  
  }
  