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How to capture all uncaucht exceptions on junit tests?

If we have created a singleton object to handle an Java Exceptions, why Thread.setDefaultUncaughtExceptionHandler runs ok in Java Application Server, Java Console Application but not works on JUnit tests?
For example, the following code works:
public class Main extends Object {
public static void main(String[] arguments) {
Thread.setDefaultUncaughtExceptionHandler(UncaughtExceptionHandler.getInstance());
double a = 1/0;
}
}
but this JUnit test not:
public class UncaughtExceptionHandlerTest {
#Test
public void throwException() {
Thread.setDefaultUncaughtExceptionHandler(UncaughtExceptionHandler.getInstance());
double a = 1/0;
}
}
but why? And, how can we solve this, to automatically handle all JUnit test exceptions without using a moody try catch to each test?

The JUnit will be catching all unexpected exceptions that are thrown by the unit tests on the unit test threads1. The normal behavior is to catch / display / record the exception as a FAILed test, and then continue with the next unit test.
This means that the there is no "uncaught exception" in the Java sense, and your uncaught exception handler is not going to be called.
It is not entirely clear what you are trying to achieve here, but I suspect that the answer would be to implement a custom runner:
https://github.com/junit-team/junit4/wiki/Test-runners
1 - If the code under test spawns its own threads, the JUnit framework has no way of knowing. It certainly cannot catch / detect uncaught exceptions on those threads. However, this doesn't seem to be what you are talking about in this question.
The main motivation, is, for example, send an e-mail or perform another administrative tasks if a junit test fail. If I have a global exception handler I could do this, instead put a catch block to each test. After the handling, maybe I will throw this exception and let junit go ahead as it does.
Well if that is what you are trying to do, then you are (IMO) doing it the wrong way. There are existing runners that provide a structured report file, or a report data structure that can give you a list of all tests that passed, failed from an assertion, failed from an exception, etc. What you should do is:
choose an appropriate runner
analyse its output
send a single email (or whatever) if there are errors that meet your criteria.
Advantages:
less effort
you deal with all errors not just uncaught exceptions (though actually assertion failures manifest as AssertionError exceptions ...)
you don't spam yourself on each and every failed test.
And there's another way. Look at JUnitCore (link). This allows you register a listener for the various test events, and then run a bunch of tests or test suites.
The other point is that you appear to be trying to duplicate (some of) the functionality of a Continuous Integration (CI) server such as Jenkins.
You then asked why this doesn't work:
#Test
public void throwException() {
Thread.setDefaultUncaughtExceptionHandler(/* some handler */));
double a = 1/0;
}
An uncaught exception handler is only invoked if nothing else catches the exception. But a typical JUnit test runner catches all exceptions that propagate from each unit test using a conventional exception handler. That means that the ArithmeticException thrown in your test never reaches your handler.

Exceptions thrown by your junit #Test method are not uncaught. JUnit catches them and uses them to fail your tests.
Now, if you had started a new Thread of your own that is not running inside JUnit's try/catch execution, a thrown exception will be essentially ignored and your test will pass.
Just think of the name... Thread.setDefaultUncaughtExceptionHandler. This only covers threads that do not explicitly have an uncaught exception handler, and then it doesn't cover exceptions that are caught by the code calling your code (JUnit, etc).
Here is relevant code from ParentRunner class:
protected final void runLeaf(Statement statement,
Description description, RunNotifier notifier) {
EachTestNotifier eachNotifier = new EachTestNotifier(notifier, description);
eachNotifier.fireTestStarted();
try {
statement.evaluate();
} catch (AssumptionViolatedException e) {
eachNotifier.addFailedAssumption(e);
} catch (Throwable e) {
eachNotifier.addFailure(e);
} finally {
eachNotifier.fireTestFinished();
}

Are you sure that jUnit isn't catching it somewhere? The method signature says that it throws Exception so I'd guess that there has to be a pretty broad catch statement up-stream.

Unit testing akka actors with JUnit

Lately I tried to write some unit tests for akka actors to test actors messages flow. I observed some strange behaviour in my tests:
Fields:
private TestActorRef<Actor> sut;
private ActorSystem system;
JavaTestKit AnotherActor;
JavaTestKit YetAnotherActor;
System and actors are created in #Before annotated method:
#Before
public void setup() throws ClassNotFoundException {
system = ActorSystem.apply();
AnotherActor = new JavaTestKit(system);
YetAnotherActor = new JavaTestKit(system);
Props props = MyActor.props(someReference);
this.sut = system.of(props, "MyActor"); }
Next
#Test
public void shouldDoSth() throws Exception {
// given actor
MyActor actor = (MyActor) sut.underlyingActor();
// when
SomeMessage message = new SomeMessage(Collections.emptyList());
sut.tell(message, AnotherActor.getRef());
// then
YetAnotherActor.expectMsgClass(
FiniteDuration.apply(1, TimeUnit.SECONDS),
YetSomeMessage.class);
}
In my code I have:
private void processMessage(SomeMessage message) {
final List<Entity> entities = message.getEntities();
if(entities.isEmpty()) {
YetAnotherActor.tell(new YetSomeMessage(), getSelf());
// return;
}
if (entities > workers.size()) {
throw new IllegalStateException("too many tasks to be started !");
}
}
Basically, sometimes (very rarely) such test fails (on another OS), and the exception from processMessage method is thrown (IllegalStateException due to business logic).
Mostly test pass as YetSomeMessage message is received by YetAnotherActor despite the fact that the IllegateStateException error is thrown as well and logged in stack trace.
As I assume from akka TestActorRef documentation:
This special ActorRef is exclusively for use during unit testing in a single-threaded environment. Therefore, it
overrides the dispatcher to CallingThreadDispatcher and sets the receiveTimeout to None. Otherwise,
it acts just like a normal ActorRef. You may retrieve a reference to the underlying actor to test internal logic.
my system is using only single thread to process messages received by actor. Could someone explain my why despite proper assertion, the test fails ?
Of course returning after sending YetSomeMessage in proper code would be done but I do not understand how another thread processing can lead to test faiulre.

Since you are using TestActorRef, you are basically doing synchronous testing. As a general rule of thumb, don't use TestActorRef unless you really need to. That thing uses the CallingThreadDispatcher, i.e. it will steal the callers thread to execute the actor. So the solution to your mystery is that the actor runs on the same thread as your test and therefore the exception ends up on the test thread.
Fortunately, this test-case of yours do not need the TestActorRef at all. You can just create the actor as an ordinary one, and everything should work (i.e. the actor will be on a proper separate thread). Please try to do everything with the asynchronous test support http://doc.akka.io/docs/akka/2.4.0/scala/testing.html#Asynchronous_Integration_Testing_with_TestKit

Adding custom messages to TestNG failures

I'm in the process of migrating a test framework from JUnit to TestNG. This framework is used to perform large end-to-end integration tests with Selenium that take several minutes to run and consist of several hundred steps across dozens of browser pages.
DISCLAIMER: I understand that this makes unit testing idealists very uneasy, but this sort of testing is required at most large service oriented companies and using unit testing tools to manage these integration tests is currently the most widespread solution. It wasn't my decision. It's what I've been asked to work on and I'm attempting to make the best of it.
At any rate, these tests fail very frequently (surprise) and making them easy to debug is of high importance. For this reason we like to detect test failures before they're reported, append some information about the failure, and then allow JUnit to fail with this extra information. For instance, without this information a failure may look like:
java.lang.<'SomeObscureException'>: <'Some obscure message'> at <'StackTrace'>
But with the added information it will look like:
java.lang.AssertionError:
Reproduction Seed: <'Random number used to generate test case'>
Country: <'Country for which test was set to run'>
Language: <'Localized language used by test'>
Step: <'Test step where the exception occurred'>
Exception Message: <'Message explaining probable cause of failure'>
Associated Exception Type: <'SomeObscureException'>
Associated Exception Message: <'Some obscure message'>
Associated Exception StackTrace: <'StackTrace'>
Exception StackTrace: <'StackTrace where we appended this information'>
It's important to note that we add this information before the test actually fails. Because our reporting tool is based entirely on the exceptions thrown by JUnit this ensures that the information we need is present in those exceptions. Ideally I'd like to add this information to an HTML or XML document using a reporter class after the test fails but before teardown is performed and then modify our reporting tool to pick up this extra information and append it to our e-mail reports. However, this has been a hard sell at our sprint planning meetings and I have not been allotted any time to work on it (running endless regressions for the developers is given higher priority than working on the test framework itself. Such is the life of the modern SDET). I also believe strongly in balance and refuse to cut into other parts of my life to get this done outside of tracked time.
What we're currently doing is this:
public class SomeTests extends TestBase {
#Test
public void someTest() {
// Test code
}
// More tests
}
public abstract class TestBase {
#Rule
public MyWatcher watcher = new MyWatcher();
// More rules and variables
#Before
public final void setup() {
// Read config, generate test data, create Selenium WebDriver, etc.
// Send references to all test objects to MyWatcher
}
}
public class MyWatcher extends TestWatcher {
// Test object references
#Override
public void failed(Throwable throwable, Description description) {
StringBuilder sb = new StringBuilder();
// Append custom test information to sb.
String exceptionSummary = sb.toString();
Assert.fail(exceptionSummary);
}
#Override
public void finished(Description description) {
// Shut down Selenium WebDriver, kill proxy server, etc.
}
// Miscellaneous teardown and logging methods
}
JUnit starts.
SomeTests inherits from TestBase class. TestBase instantiates our own instance of a TestWatcher via #Rule annotation (MyWatcher).
Test setup is run in TestBase class.
References to test objects are sent to MyWatcher.
JUnit begins someTest() method.
someTest fails at some point.
JUnit calls overridden failed() method in MyWatcher.
failed() method appends custom test information to new message using references passed by TestBase.
failed() method calls JUnit's Assert.fail() method with the customized message.
JUnit throws a java.lang.Assertion error for this new failure with the customized message. This is the exception that actually gets recorded in the test results.
JUnit calls overridden finished() method.
finished() method performs test teardown.
Our reporting tool picks up the summarized errors thrown by JUnit, and includes them in the e-mails we receive. This makes life easier than debugging the original exceptions would be without any of the extra information added by MyWatcher after the original failure.
I'd now like to implement a similar mechanism using TestNG. I first tried adding an IInvokedMethodListener in a #Listener annotation to our TestBase class as a way of replacing the TestWatcher that we were using in JUnit. Unfortunately the methods in this listener were getting called after every #BeforeMethod and #AfterMethod call as well as for the actual tests. This was causing quite a mess when I called Assert.fail from inside the IInvokedMethodListener so I opted to scrap this approach and insert the code directly into an #AfterMethod call in our TestBase class.
Unfortunately TestNG does not appear to handle the 'failing twice' approach that we were using in JUnit. When I call Assert.fail in the #AfterMethod of a test that has already failed it gets reported as an additional failure. It seems like we're going to have to come up with another way of doing this until I can get authorization to write a proper test reporter that includes the information we need for debugging.
In the meantime, we still need to dress up the exceptions that get thrown by TestNG so that the debugging information will appear in our e-mail reports. One idea I have for doing this is to wrap every single test in a try/catch block. If the test fails (an exception gets thrown), then we can catch that exception, dress it up in a summary exception with the debugging information added to that exception's message, and call Assert.fail with our new summarized exception. That way TestNG only ever sees that one exception and should only report one failure. This feels like a kludge on top of a kludge though, and I can't help but feel that there's a better way of doing this.
Does anybody know of a better method for modifying what gets reported by TestNG? Is there some kind of trick I can use for replacing the original exception with my own using ITestContext or ITestResult? Can I dive in somewhere and remove the original failure from some list, or is it already too late to stop TestNG's internal reporting by the time I get to the #AfterMethod functions?
Do you have any other advice regarding this sort of testing or exception handling in general? I don't have many knowledgeable co-workers to help with this stuff so I'm pretty much just winging it.

Implement IInvokedMethodListener:
public class InvokedMethodListener implements IInvokedMethodListener {
#Override
public void beforeInvocation(IInvokedMethod method, ITestResult testResult) {
}
#Override
public void afterInvocation(IInvokedMethod method, ITestResult result) {
if (method.isTestMethod() && ITestResult.FAILURE == result.getStatus()) {
Throwable throwable = result.getThrowable();
String originalMessage = throwable.getMessage();
String newMessage = originalMessage + "\nReproduction Seed: ...\nCountry: ...";
try {
FieldUtils.writeField(throwable, "detailMessage", newMessage, true);
} catch (Exception e) {
e.printStackTrace();
}
}
}
}
Register it in your test:
#Listeners(InvokedMethodListener.class)
public class YourTest {
#Test
public void test() {
Assert.fail("some message");
}
}
or in testng.xml.
If you execute it, you should get:
java.lang.AssertionError: some message
Reproduction Seed: ...
Country: ...

You can user SoftAssert Class in testNG for implementing above scenario. SoftAssert Class has an hash map array which stores all the error message from Asserts in test cases and prints them in the end of the test case. you can also extend Assertion class to implement methods as per your requirement.
More information regarding SoftAssert class and its implementation can be found here

JUnit4 : Test a shutdown hook is called

I have a method which adds a shutdown hook. I need to test (via JUnit) that the code executed in the hook is called :
public void myMethod(){
Runtime.getRuntime().addShutdownHook(new Thread() {
#Override
public void run() {
... code to test ...
}
});
}
How can I simulate a shutdown in my unit test ?

I don't think you'll be able to test that. Instead, just test that your code behaves correctly when invoked (by unit testing it separately). Then, trust that Java will invoke your code at the right time.
I.e. extract your code into a separate class that extends Thread and test the behaviour by executing run() in a unit test.

In addition to Duncans answer I'd like to point out the Runtime.getRuntime().removeShutdownHook(Thread) method. Its boolean return value indicates if the respective thread was a registered hook previously.
Thus, one can test if the hook' run() method performs correctly as one part of a test.
As a second part one can call Runtime.getRuntime().removeShutdownHook(Thread)` and assert that the thread was actually registered as a hook.
Together, the two tests assure the overall functioning of the shutdown hook.

How do you customize exception handling behavior in JUnit 3?

I want to implement exception checking (like in JUnit 4) using JUnit 3. For example, I would like to be able to write tests like this:
public void testMyExceptionThrown() throws Exception {
shouldThrow(MyException.class);
doSomethingThatMightThrowMyException();
}
This should succeed if and only if a MyException is thrown.
There is the ExceptionTestCase class in JUnit, but but I want something that each test* method can decide to use or not use. What is the best way to achieve this?

Would the solution:
public void testMyExceptionThrown() throws Exception {
try {
doSomethingThatMightThrowMyException();
fail("Expected Exception MyException");
} catch(MyException e) {
// do nothing, it's OK
}
}
be suitable for what you're thinking of?
Also have a look at this thread, where someone created a Proxy-solution for JUnit3 which seems to be another possibility to solve your problem.

There is no need to implement your own solution because there is already one that can be used with JUnit3 (and any other testing framework): catch-exception.

The simplest approach is to use the Execute Around idiom to abstract away the try-catch that you would usually write.
More sophisticated is to note that TestCase is just a Test. I forget the details, but we can override the execution of the test (which the framework initially calls through run(TestResult) specified in Test). In that override we can place the try-catch, as per Execute Around. The testXxx method should call a set method to install the expected exception type.