test/tck/BlockingQueueTest.java

/*
 * Written by Doug Lea and Martin Buchholz with assistance from members
 * of JCP JSR-166 Expert Group and released to the public domain, as
 * explained at http://creativecommons.org/publicdomain/zero/1.0/
 *
 * Other contributors include Andrew Wright, Jeffrey Hayes,
 * Pat Fisher, Mike Judd.
 */

import static java.util.concurrent.TimeUnit.MILLISECONDS;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collection;
import java.util.Queue;
import java.util.concurrent.BlockingQueue;
import java.util.concurrent.CountDownLatch;

import junit.framework.Test;
import junit.framework.TestSuite;

/**
 * Contains "contract" tests applicable to all BlockingQueue implementations.
 */
public abstract class BlockingQueueTest extends JSR166TestCase {
    /*
     * This is the start of an attempt to refactor the tests for the
     * various related implementations of related interfaces without
     * too much duplicated code.  junit does not really support such
     * testing.  Here subclasses of TestCase not only contain tests,
     * but also configuration information that describes the
     * implementation class, most importantly how to instantiate
     * instances.
     */

    /** Like suite(), but non-static */
    public Test testSuite() {
        // TODO: filter the returned tests using the configuration
        // information provided by the subclass via protected methods.
        return new TestSuite(this.getClass());
    }

    //----------------------------------------------------------------
    // Configuration methods
    //----------------------------------------------------------------

    /** Returns an empty instance of the implementation class. */
    protected abstract BlockingQueue emptyCollection();

    /**
     * Returns an element suitable for insertion in the collection.
     * Override for collections with unusual element types.
     */
    protected Object makeElement(int i) {
        return Integer.valueOf(i);
    }

    //----------------------------------------------------------------
    // Tests
    //----------------------------------------------------------------

    /**
     * offer(null) throws NullPointerException
     */
    public void testOfferNull() {
        final Queue q = emptyCollection();
        try {
            q.offer(null);
            shouldThrow();
        } catch (NullPointerException success) {}
    }

    /**
     * add(null) throws NullPointerException
     */
    public void testAddNull() {
        final Collection q = emptyCollection();
        try {
            q.add(null);
            shouldThrow();
        } catch (NullPointerException success) {}
    }

    /**
     * timed offer(null) throws NullPointerException
     */
    public void testTimedOfferNull() throws InterruptedException {
        final BlockingQueue q = emptyCollection();
        long startTime = System.nanoTime();
        try {
            q.offer(null, LONG_DELAY_MS, MILLISECONDS);
            shouldThrow();
        } catch (NullPointerException success) {}
        assertTrue(millisElapsedSince(startTime) < LONG_DELAY_MS);
    }

    /**
     * put(null) throws NullPointerException
     */
    public void testPutNull() throws InterruptedException {
        final BlockingQueue q = emptyCollection();
        try {
            q.put(null);
            shouldThrow();
        } catch (NullPointerException success) {}
    }

    /**
     * addAll(null) throws NullPointerException
     */
    public void testAddAllNull() throws InterruptedException {
        final Collection q = emptyCollection();
        try {
            q.addAll(null);
            shouldThrow();
        } catch (NullPointerException success) {}
    }

    /**
     * addAll of a collection with null elements throws NullPointerException
     */
    public void testAddAllNullElements() {
        final Collection q = emptyCollection();
        final Collection<Integer> elements = Arrays.asList(new Integer[SIZE]);
        try {
            q.addAll(elements);
            shouldThrow();
        } catch (NullPointerException success) {}
    }

    /**
     * toArray(null) throws NullPointerException
     */
    public void testToArray_NullArray() {
        final Collection q = emptyCollection();
        try {
            q.toArray(null);
            shouldThrow();
        } catch (NullPointerException success) {}
    }

    /**
     * drainTo(null) throws NullPointerException
     */
    public void testDrainToNull() {
        final BlockingQueue q = emptyCollection();
        try {
            q.drainTo(null);
            shouldThrow();
        } catch (NullPointerException success) {}
    }

    /**
     * drainTo(this) throws IllegalArgumentException
     */
    public void testDrainToSelf() {
        final BlockingQueue q = emptyCollection();
        try {
            q.drainTo(q);
            shouldThrow();
        } catch (IllegalArgumentException success) {}
    }

    /**
     * drainTo(null, n) throws NullPointerException
     */
    public void testDrainToNullN() {
        final BlockingQueue q = emptyCollection();
        try {
            q.drainTo(null, 0);
            shouldThrow();
        } catch (NullPointerException success) {}
    }

    /**
     * drainTo(this, n) throws IllegalArgumentException
     */
    public void testDrainToSelfN() {
        final BlockingQueue q = emptyCollection();
        try {
            q.drainTo(q, 0);
            shouldThrow();
        } catch (IllegalArgumentException success) {}
    }

    /**
     * drainTo(c, n) returns 0 and does nothing when n <= 0
     */
    public void testDrainToNonPositiveMaxElements() {
        final BlockingQueue q = emptyCollection();
        final int[] ns = { 0, -1, -42, Integer.MIN_VALUE };
        final ArrayList sink = new ArrayList();
        for (int n : ns) {
            assertEquals(0, q.drainTo(sink, n));
            assertTrue(sink.isEmpty());
        }
        if (q.remainingCapacity() > 0) {
            // Not SynchronousQueue, that is
            Object one = makeElement(1);
            q.add(one);
            for (int n : ns)
                assertEquals(0, q.drainTo(sink, n));
            assertEquals(1, q.size());
            assertSame(one, q.poll());
            assertTrue(sink.isEmpty());
        }
    }

    /**
     * timed poll before a delayed offer times out; after offer succeeds;
     * on interruption throws
     */
    public void testTimedPollWithOffer() throws InterruptedException {
        final BlockingQueue q = emptyCollection();
        final CheckedBarrier barrier = new CheckedBarrier(2);
        final Object zero = makeElement(0);
        Thread t = newStartedThread(new CheckedRunnable() {
            public void realRun() throws InterruptedException {
                long startTime = System.nanoTime();
                assertNull(q.poll(timeoutMillis(), MILLISECONDS));
                assertTrue(millisElapsedSince(startTime) >= timeoutMillis());

                barrier.await();

                assertSame(zero, q.poll(LONG_DELAY_MS, MILLISECONDS));

                Thread.currentThread().interrupt();
                try {
                    q.poll(LONG_DELAY_MS, MILLISECONDS);
                    shouldThrow();
                } catch (InterruptedException success) {}
                assertFalse(Thread.interrupted());

                barrier.await();
                try {
                    q.poll(LONG_DELAY_MS, MILLISECONDS);
                    shouldThrow();
                } catch (InterruptedException success) {}
                assertFalse(Thread.interrupted());

                assertTrue(millisElapsedSince(startTime) < LONG_DELAY_MS);
            }});

        barrier.await();
        long startTime = System.nanoTime();
        assertTrue(q.offer(zero, LONG_DELAY_MS, MILLISECONDS));
        assertTrue(millisElapsedSince(startTime) < LONG_DELAY_MS);

        barrier.await();
        assertThreadBlocks(t, Thread.State.TIMED_WAITING);
        t.interrupt();
        awaitTermination(t);
    }

    /**
     * take() blocks interruptibly when empty
     */
    public void testTakeFromEmptyBlocksInterruptibly() {
        final BlockingQueue q = emptyCollection();
        final CountDownLatch threadStarted = new CountDownLatch(1);
        Thread t = newStartedThread(new CheckedRunnable() {
            public void realRun() {
                threadStarted.countDown();
                try {
                    q.take();
                    shouldThrow();
                } catch (InterruptedException success) {}
                assertFalse(Thread.interrupted());
            }});

        await(threadStarted);
        assertThreadBlocks(t, Thread.State.WAITING);
        t.interrupt();
        awaitTermination(t);
    }

    /**
     * take() throws InterruptedException immediately if interrupted
     * before waiting
     */
    public void testTakeFromEmptyAfterInterrupt() {
        final BlockingQueue q = emptyCollection();
        Thread t = newStartedThread(new CheckedRunnable() {
            public void realRun() {
                Thread.currentThread().interrupt();
                try {
                    q.take();
                    shouldThrow();
                } catch (InterruptedException success) {}
                assertFalse(Thread.interrupted());
            }});

        awaitTermination(t);
    }

    /**
     * timed poll() blocks interruptibly when empty
     */
    public void testTimedPollFromEmptyBlocksInterruptibly() {
        final BlockingQueue q = emptyCollection();
        final CountDownLatch threadStarted = new CountDownLatch(1);
        Thread t = newStartedThread(new CheckedRunnable() {
            public void realRun() {
                threadStarted.countDown();
                try {
                    q.poll(2 * LONG_DELAY_MS, MILLISECONDS);
                    shouldThrow();
                } catch (InterruptedException success) {}
                assertFalse(Thread.interrupted());
            }});

        await(threadStarted);
        assertThreadBlocks(t, Thread.State.TIMED_WAITING);
        t.interrupt();
        awaitTermination(t);
    }

    /**
     * timed poll() throws InterruptedException immediately if
     * interrupted before waiting
     */
    public void testTimedPollFromEmptyAfterInterrupt() {
        final BlockingQueue q = emptyCollection();
        Thread t = newStartedThread(new CheckedRunnable() {
            public void realRun() {
                Thread.currentThread().interrupt();
                try {
                    q.poll(2 * LONG_DELAY_MS, MILLISECONDS);
                    shouldThrow();
                } catch (InterruptedException success) {}
                assertFalse(Thread.interrupted());
            }});

        awaitTermination(t);
    }

    /**
     * remove(x) removes x and returns true if present
     * TODO: move to superclass CollectionTest.java
     */
    public void testRemoveElement() {
        final BlockingQueue q = emptyCollection();
        final int size = Math.min(q.remainingCapacity(), SIZE);
        final Object[] elts = new Object[size];
        assertFalse(q.contains(makeElement(99)));
        assertFalse(q.remove(makeElement(99)));
        checkEmpty(q);
        for (int i = 0; i < size; i++)
            q.add(elts[i] = makeElement(i));
        for (int i = 1; i < size; i += 2) {
            for (int pass = 0; pass < 2; pass++) {
                assertEquals((pass == 0), q.contains(elts[i]));
                assertEquals((pass == 0), q.remove(elts[i]));
                assertFalse(q.contains(elts[i]));
                assertTrue(q.contains(elts[i - 1]));
                if (i < size - 1)
                    assertTrue(q.contains(elts[i + 1]));
            }
        }
        if (size > 0)
            assertTrue(q.contains(elts[0]));
        for (int i = size - 2; i >= 0; i -= 2) {
            assertTrue(q.contains(elts[i]));
            assertFalse(q.contains(elts[i + 1]));
            assertTrue(q.remove(elts[i]));
            assertFalse(q.contains(elts[i]));
            assertFalse(q.remove(elts[i + 1]));
            assertFalse(q.contains(elts[i + 1]));
        }
        checkEmpty(q);
    }

    /** For debugging. */
    public void XXXXtestFails() {
        fail(emptyCollection().getClass().toString());
    }

}
Revision:	1.21
Committed:	Wed Jan 10 14:41:52 2018 UTC (6 years, 4 months ago) by jsr166
Branch:	MAIN
Changes since 1.20:	+7 -5 lines
Log Message:	testDrainToNonPositiveMaxElements: check that sink is unchanged
#	User	Rev	Content
1	jsr166	1.1	/*
2			* Written by Doug Lea and Martin Buchholz with assistance from members
3			* of JCP JSR-166 Expert Group and released to the public domain, as
4	jsr166	1.5	* explained at http://creativecommons.org/publicdomain/zero/1.0/
5	jsr166	1.1	*
6			* Other contributors include Andrew Wright, Jeffrey Hayes,
7			* Pat Fisher, Mike Judd.
8			*/
9
10	jsr166	1.13	import static java.util.concurrent.TimeUnit.MILLISECONDS;
11
12	jsr166	1.10	import java.util.ArrayList;
13	jsr166	1.8	import java.util.Arrays;
14			import java.util.Collection;
15			import java.util.Queue;
16			import java.util.concurrent.BlockingQueue;
17			import java.util.concurrent.CountDownLatch;
18	jsr166	1.13
19			import junit.framework.Test;
20			import junit.framework.TestSuite;
21	jsr166	1.1
22			/**
23	jsr166	1.8	* Contains "contract" tests applicable to all BlockingQueue implementations.
24	jsr166	1.1	*/
25			public abstract class BlockingQueueTest extends JSR166TestCase {
26			/*
27			* This is the start of an attempt to refactor the tests for the
28			* various related implementations of related interfaces without
29			* too much duplicated code. junit does not really support such
30			* testing. Here subclasses of TestCase not only contain tests,
31			* but also configuration information that describes the
32			* implementation class, most importantly how to instantiate
33			* instances.
34			*/
35
36			/** Like suite(), but non-static */
37			public Test testSuite() {
38			// TODO: filter the returned tests using the configuration
39			// information provided by the subclass via protected methods.
40			return new TestSuite(this.getClass());
41			}
42
43	jsr166	1.8	//----------------------------------------------------------------
44			// Configuration methods
45			//----------------------------------------------------------------
46	jsr166	1.9
47	jsr166	1.1	/** Returns an empty instance of the implementation class. */
48			protected abstract BlockingQueue emptyCollection();
49
50			/**
51	jsr166	1.8	* Returns an element suitable for insertion in the collection.
52			* Override for collections with unusual element types.
53			*/
54			protected Object makeElement(int i) {
55			return Integer.valueOf(i);
56			}
57
58			//----------------------------------------------------------------
59			// Tests
60			//----------------------------------------------------------------
61	jsr166	1.9
62	jsr166	1.8	/**
63			* offer(null) throws NullPointerException
64			*/
65			public void testOfferNull() {
66			final Queue q = emptyCollection();
67			try {
68			q.offer(null);
69			shouldThrow();
70			} catch (NullPointerException success) {}
71			}
72
73			/**
74			* add(null) throws NullPointerException
75			*/
76			public void testAddNull() {
77			final Collection q = emptyCollection();
78			try {
79			q.add(null);
80			shouldThrow();
81			} catch (NullPointerException success) {}
82			}
83
84			/**
85			* timed offer(null) throws NullPointerException
86			*/
87			public void testTimedOfferNull() throws InterruptedException {
88			final BlockingQueue q = emptyCollection();
89			long startTime = System.nanoTime();
90			try {
91			q.offer(null, LONG_DELAY_MS, MILLISECONDS);
92			shouldThrow();
93			} catch (NullPointerException success) {}
94			assertTrue(millisElapsedSince(startTime) < LONG_DELAY_MS);
95			}
96
97			/**
98			* put(null) throws NullPointerException
99			*/
100			public void testPutNull() throws InterruptedException {
101			final BlockingQueue q = emptyCollection();
102			try {
103			q.put(null);
104			shouldThrow();
105			} catch (NullPointerException success) {}
106			}
107
108			/**
109	jsr166	1.20	* addAll(null) throws NullPointerException
110	jsr166	1.8	*/
111			public void testAddAllNull() throws InterruptedException {
112			final Collection q = emptyCollection();
113			try {
114			q.addAll(null);
115			shouldThrow();
116			} catch (NullPointerException success) {}
117			}
118
119			/**
120			* addAll of a collection with null elements throws NullPointerException
121			*/
122			public void testAddAllNullElements() {
123			final Collection q = emptyCollection();
124			final Collection<Integer> elements = Arrays.asList(new Integer[SIZE]);
125			try {
126			q.addAll(elements);
127			shouldThrow();
128			} catch (NullPointerException success) {}
129			}
130
131			/**
132			* toArray(null) throws NullPointerException
133			*/
134			public void testToArray_NullArray() {
135			final Collection q = emptyCollection();
136			try {
137			q.toArray(null);
138			shouldThrow();
139			} catch (NullPointerException success) {}
140			}
141
142			/**
143			* drainTo(null) throws NullPointerException
144			*/
145			public void testDrainToNull() {
146			final BlockingQueue q = emptyCollection();
147			try {
148			q.drainTo(null);
149			shouldThrow();
150			} catch (NullPointerException success) {}
151			}
152
153			/**
154			* drainTo(this) throws IllegalArgumentException
155			*/
156			public void testDrainToSelf() {
157			final BlockingQueue q = emptyCollection();
158			try {
159			q.drainTo(q);
160			shouldThrow();
161			} catch (IllegalArgumentException success) {}
162			}
163
164			/**
165			* drainTo(null, n) throws NullPointerException
166			*/
167			public void testDrainToNullN() {
168			final BlockingQueue q = emptyCollection();
169			try {
170			q.drainTo(null, 0);
171			shouldThrow();
172			} catch (NullPointerException success) {}
173			}
174
175			/**
176			* drainTo(this, n) throws IllegalArgumentException
177			*/
178			public void testDrainToSelfN() {
179			final BlockingQueue q = emptyCollection();
180			try {
181			q.drainTo(q, 0);
182			shouldThrow();
183			} catch (IllegalArgumentException success) {}
184			}
185
186			/**
187	jsr166	1.11	* drainTo(c, n) returns 0 and does nothing when n <= 0
188	jsr166	1.10	*/
189	jsr166	1.11	public void testDrainToNonPositiveMaxElements() {
190	jsr166	1.10	final BlockingQueue q = emptyCollection();
191	jsr166	1.11	final int[] ns = { 0, -1, -42, Integer.MIN_VALUE };
192	jsr166	1.21	final ArrayList sink = new ArrayList();
193			for (int n : ns) {
194			assertEquals(0, q.drainTo(sink, n));
195			assertTrue(sink.isEmpty());
196			}
197	jsr166	1.11	if (q.remainingCapacity() > 0) {
198			// Not SynchronousQueue, that is
199	jsr166	1.10	Object one = makeElement(1);
200			q.add(one);
201	jsr166	1.11	for (int n : ns)
202	jsr166	1.21	assertEquals(0, q.drainTo(sink, n));
203	jsr166	1.10	assertEquals(1, q.size());
204			assertSame(one, q.poll());
205	jsr166	1.21	assertTrue(sink.isEmpty());
206	jsr166	1.10	}
207			}
208
209			/**
210	jsr166	1.7	* timed poll before a delayed offer times out; after offer succeeds;
211	jsr166	1.1	* on interruption throws
212			*/
213			public void testTimedPollWithOffer() throws InterruptedException {
214			final BlockingQueue q = emptyCollection();
215			final CheckedBarrier barrier = new CheckedBarrier(2);
216	jsr166	1.8	final Object zero = makeElement(0);
217	jsr166	1.1	Thread t = newStartedThread(new CheckedRunnable() {
218			public void realRun() throws InterruptedException {
219	jsr166	1.7	long startTime = System.nanoTime();
220			assertNull(q.poll(timeoutMillis(), MILLISECONDS));
221			assertTrue(millisElapsedSince(startTime) >= timeoutMillis());
222	jsr166	1.1
223			barrier.await();
224	jsr166	1.7
225			assertSame(zero, q.poll(LONG_DELAY_MS, MILLISECONDS));
226	jsr166	1.1
227			Thread.currentThread().interrupt();
228			try {
229	jsr166	1.7	q.poll(LONG_DELAY_MS, MILLISECONDS);
230	jsr166	1.1	shouldThrow();
231			} catch (InterruptedException success) {}
232	jsr166	1.7	assertFalse(Thread.interrupted());
233	jsr166	1.1
234			barrier.await();
235			try {
236	jsr166	1.7	q.poll(LONG_DELAY_MS, MILLISECONDS);
237	jsr166	1.1	shouldThrow();
238			} catch (InterruptedException success) {}
239	jsr166	1.7	assertFalse(Thread.interrupted());
240	jsr166	1.17
241			assertTrue(millisElapsedSince(startTime) < LONG_DELAY_MS);
242	jsr166	1.1	}});
243
244			barrier.await();
245	jsr166	1.7	long startTime = System.nanoTime();
246			assertTrue(q.offer(zero, LONG_DELAY_MS, MILLISECONDS));
247			assertTrue(millisElapsedSince(startTime) < LONG_DELAY_MS);
248
249	jsr166	1.1	barrier.await();
250	jsr166	1.19	assertThreadBlocks(t, Thread.State.TIMED_WAITING);
251	jsr166	1.1	t.interrupt();
252	jsr166	1.7	awaitTermination(t);
253	jsr166	1.1	}
254
255	jsr166	1.2	/**
256	jsr166	1.3	* take() blocks interruptibly when empty
257	jsr166	1.2	*/
258	jsr166	1.7	public void testTakeFromEmptyBlocksInterruptibly() {
259	jsr166	1.2	final BlockingQueue q = emptyCollection();
260			final CountDownLatch threadStarted = new CountDownLatch(1);
261			Thread t = newStartedThread(new CheckedRunnable() {
262			public void realRun() {
263			threadStarted.countDown();
264			try {
265			q.take();
266			shouldThrow();
267			} catch (InterruptedException success) {}
268	jsr166	1.7	assertFalse(Thread.interrupted());
269	jsr166	1.2	}});
270	jsr166	1.3
271	jsr166	1.7	await(threadStarted);
272	jsr166	1.18	assertThreadBlocks(t, Thread.State.WAITING);
273	jsr166	1.2	t.interrupt();
274	jsr166	1.7	awaitTermination(t);
275	jsr166	1.3	}
276
277			/**
278			* take() throws InterruptedException immediately if interrupted
279			* before waiting
280			*/
281	jsr166	1.7	public void testTakeFromEmptyAfterInterrupt() {
282	jsr166	1.3	final BlockingQueue q = emptyCollection();
283			Thread t = newStartedThread(new CheckedRunnable() {
284			public void realRun() {
285			Thread.currentThread().interrupt();
286			try {
287			q.take();
288			shouldThrow();
289			} catch (InterruptedException success) {}
290	jsr166	1.7	assertFalse(Thread.interrupted());
291			}});
292
293			awaitTermination(t);
294			}
295
296			/**
297			* timed poll() blocks interruptibly when empty
298			*/
299			public void testTimedPollFromEmptyBlocksInterruptibly() {
300			final BlockingQueue q = emptyCollection();
301			final CountDownLatch threadStarted = new CountDownLatch(1);
302			Thread t = newStartedThread(new CheckedRunnable() {
303			public void realRun() {
304			threadStarted.countDown();
305			try {
306			q.poll(2 * LONG_DELAY_MS, MILLISECONDS);
307			shouldThrow();
308			} catch (InterruptedException success) {}
309			assertFalse(Thread.interrupted());
310			}});
311
312			await(threadStarted);
313	jsr166	1.18	assertThreadBlocks(t, Thread.State.TIMED_WAITING);
314	jsr166	1.7	t.interrupt();
315			awaitTermination(t);
316			}
317
318			/**
319			* timed poll() throws InterruptedException immediately if
320			* interrupted before waiting
321			*/
322			public void testTimedPollFromEmptyAfterInterrupt() {
323			final BlockingQueue q = emptyCollection();
324			Thread t = newStartedThread(new CheckedRunnable() {
325			public void realRun() {
326			Thread.currentThread().interrupt();
327			try {
328			q.poll(2 * LONG_DELAY_MS, MILLISECONDS);
329			shouldThrow();
330			} catch (InterruptedException success) {}
331			assertFalse(Thread.interrupted());
332	jsr166	1.3	}});
333
334	jsr166	1.7	awaitTermination(t);
335	jsr166	1.2	}
336
337	jsr166	1.12	/**
338			* remove(x) removes x and returns true if present
339			* TODO: move to superclass CollectionTest.java
340			*/
341			public void testRemoveElement() {
342			final BlockingQueue q = emptyCollection();
343			final int size = Math.min(q.remainingCapacity(), SIZE);
344			final Object[] elts = new Object[size];
345			assertFalse(q.contains(makeElement(99)));
346			assertFalse(q.remove(makeElement(99)));
347			checkEmpty(q);
348			for (int i = 0; i < size; i++)
349			q.add(elts[i] = makeElement(i));
350	jsr166	1.14	for (int i = 1; i < size; i += 2) {
351	jsr166	1.12	for (int pass = 0; pass < 2; pass++) {
352			assertEquals((pass == 0), q.contains(elts[i]));
353			assertEquals((pass == 0), q.remove(elts[i]));
354			assertFalse(q.contains(elts[i]));
355	jsr166	1.16	assertTrue(q.contains(elts[i - 1]));
356	jsr166	1.12	if (i < size - 1)
357	jsr166	1.16	assertTrue(q.contains(elts[i + 1]));
358	jsr166	1.12	}
359			}
360			if (size > 0)
361			assertTrue(q.contains(elts[0]));
362	jsr166	1.15	for (int i = size - 2; i >= 0; i -= 2) {
363	jsr166	1.12	assertTrue(q.contains(elts[i]));
364	jsr166	1.16	assertFalse(q.contains(elts[i + 1]));
365	jsr166	1.12	assertTrue(q.remove(elts[i]));
366			assertFalse(q.contains(elts[i]));
367	jsr166	1.16	assertFalse(q.remove(elts[i + 1]));
368			assertFalse(q.contains(elts[i + 1]));
369	jsr166	1.12	}
370			checkEmpty(q);
371			}
372
373	jsr166	1.1	/** For debugging. */
374			public void XXXXtestFails() {
375			fail(emptyCollection().getClass().toString());
376			}
377
378			}