Unit testingconcurrent code

public class FlawedList<T> extends ArrayList<T> { public boolean putIfAbsent(T object) { boolean absent = !super.contains(object); if (absent) { super.add(object); } return absent; }}

Implementing a broken unique list

@Testpublic void testPutIfAbsent() { FlawedList<String> list = new FlawedList<String>(); list.putIfAbsent("foo"); list.putIfAbsent("foo"); assertThat(list.size(), is(1)); }

JUnit

FlawedList<String> list = new FlawedList<String>();

@Test(threadPoolSize = 5, invocationCount = 20) public void testList() { list.putIfAbsent("foo"); assertThat(list.size(), is(1)); }

TestNG

TestNG with breakpoints

public class FlawedList<T> extends ArrayList<T> { public boolean putIfAbsent(T object) { boolean absent = !super.contains(object); if (absent) { super.add(object); } return absent; }}

FlawedList<String> list = new FlawedList<String>();

@Test(threadPoolSize = 5, invocationCount = 20) public void testList() { list.putIfAbsent("foo"); assertThat(list.size(), is(1)); }

public boolean putIfAbsent(T object) { boolean absent = !super.contains(object); if (absent) { super.add(object); } return absent; }

Testing with break points: first weaving

FlawedList["foo", "foo"]FlawedList["foo"]FlawedList[]

Testing with break points: second weaving

Thread 1Thread 2

Legend:

ThreadWeaver

absent

true

falsetrue

public class WeavedFlawedListTest { private FlawedList<String> list;

@ThreadedBefore public void before() { list = new FlawedList<String>(); }

@ThreadedMain public void mainThread() { list.putIfAbsent("foo"); } @ThreadedSecondary public void secondThread() { list.putIfAbsent("foo"); }

@ThreadedAfter public void after() { assertEquals(1, list.size()); } }

ThreadWeaver (https://code.google.com/p/thread-weaver)

Seamless JUnit integration

public class MyListTest {

@Test public void testFlawedList() { AnnotatedTestRunner runner = new AnnotatedTestRunner(); runner.runTests(getClass(), FlawedList.class); }

// put method with @Threaded<...> annotations here}

@Test public void testFlawedList() { AnnotatedTestRunner runner = new AnnotatedTestRunner(); runner.runTests(getClass(), FlawedList.class); }

How does it work?

Instrumented code:

public boolean putIfAbsent(T object) { Framework.considerBreakpoint(Thread.currentThread(), 0); boolean absent = !super.contains(object); Framework.considerBreakpoint(Thread.currentThread(), 1); if (absent) { Framework.considerBreakpoint(Thread.currentThread(), 2); super.add(object); } Framework.considerBreakpoint(Thread.currentThread(), 3); return absent; }

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