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POUnit test for Handler postDelayed() on Android
 

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  1. POUnit test for Handler postDelayed() on Android
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    <p>I am writing a simple class for an Android app to act as a timer which will update the Activity UI at regular intervals. The timer class is using a Handler postDelayed() function to execute a Runnable.</p> <p>Here's timer the code:</p> <pre><code>public class MyTimer { private MyTimerDelegate _delegate; private int _seconds = 0; public MyTimerDelegate delegate() { return _delegate; } public void setDelegate(MyTimerDelegate delegate) { _delegate = delegate; } public int seconds() { return _seconds; } public void setSeconds(int seconds) { if (seconds &lt; 0) throw new IllegalArgumentException(); _seconds = seconds; } public void start() throws Exception { if (_delegate == null) throw new Exception("A delegate has not been set."); _delegate.MyTimerStartedFromSeconds(this, _seconds); // Schedule the first timer fire. final Handler handler = new Handler(); final MyTimer MyTimer = this; handler.postDelayed(new Runnable() { @Override public void run() { // The timer fired. Decrement seconds. _seconds -= 1; // Inform the delegate. _delegate.MyTimer_countedDownToSeconds(MyTimer, _seconds); // If there are seconds remaining, schedule the next fire. // Otherwise, stop the timer. if (_seconds &gt; 0) { handler.postDelayed(this, 1000); } else { _delegate.MyTimerStopped(MyTimer); } } }, 1000); } } </code></pre> <p>My questions is: <strong>How can I write a JUnit 4 test to ensure that MyTimer is calling its delegate at each interval during the count down?</strong></p> <p>Here's what I have done so far:</p> <pre><code>public void testCountdownCallsDelegate() throws Exception { class MockMyTimerDelegate implements MyTimerDelegate { public int callbackCount = 0; @Override public void biteTimerStartedFromSeconds(BiteTimer biteTimer, int seconds) { } @Override public void biteTimerStopped(BiteTimer biteTimer) { } @Override public void biteTimer_countedDownToSeconds(BiteTimer biteTimer, int seconds) { callbackCount++; } } MockMyTimerDelegate delegate = new MockMyTimerDelegate(); MyTimer timer = new MyTimer(); timer.setDelegate(delegate); timer.setSeconds(1); timer.start(); // Need some way to wait here and allow the timer to call its delegate... assertEquals("The timer should have called the delegate when counting down.", 1, delegate.callbackCount); } </code></pre> <p>Obviously, I cannot block the thread with Thread.sleep() calls. Any ideas?</p> <p><strong>Found solution</strong></p> <p>This solution seems to work. I'm posting it here in case it helps someone else. Please improve it if you see ways to.</p> <pre><code>public void testMyTimerDelegateIsCalledForEachSecondDuringCountdown() throws Exception { // An object to sync our threads with. Object syncLock = new Object(); // This thread class will perform the actual test. class TimerThread extends Thread { Object _syncLock; TimerThread(Object syncLock) { _syncLock = syncLock; } @Override public void run() { // Since MyTimer is calling Handler postDelayed(), we need a Looper. Looper.prepare(); // myTimer was instantiated in setUp() myTimer.setDelegate(new MockMyTimerDelegate() { @Override public void myTimer_countedDownToSeconds(MyTimer myTimer, int seconds) { countdownToSecondsCallCount++; if (countdownToSecondsCallCount &gt;= 3) { synchronized (_syncLock) { // The test is complete. Now the parent thread can continue and assert the results. _syncLock.notify(); } } } }); myTimer.setSeconds(3); try { myTimer.start(); Looper.loop(); } catch (Exception e) { } } } // Run the test on its own thread and wait for it to finish. TimerThread t = new TimerThread(syncLock); t.start(); synchronized (syncLock) { // Wait more time than should be needed, but timeout in case of failure. syncLock.wait(5000); } assertEquals("MyTimerDelegate should have been called 3 times during three second countdown.", 3, ((MockMyTimerDelegate) myTimer.delegate()).countdownToSecondsCallCount); } </code></pre>
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    1. USEric Baker
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    1. COIt seems I didn't look hard enough for similar questions. This post answers my question: http://stackoverflow.com/questions/7715978/android-unit-tests-with-multiple-threads
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      1. USEric Baker
 

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