How to test exception scenario in junit 5 in spring boot?

Question

I have a void method that does some tasks trying to test exception scenarios but the test case is getting failed.

public void completetask(){
   try{
     RemoteUser rm = usrRepo.findById(12);
     assistenRepo.save(rm);
   }catch(Exception e){
    log.error("Exception occurred while making changes {}", e,getMessage());
   }
}

How can we test the exception scenario here on JUnit 5?

I have tried this but it's not working


@Test
public void completetaskTest(){
    RemoteUser rm = getDummyRemoteUsr();
    Mockito.when(usrRepo.findById(12)).thenReturn(rm);
    Mockito.when(assistenRepo.save(rm)).thenThrow(new Exception("Error Abnormal"));
    Exception exception = Assestions.assertThrow(Exception.class, () -> usrService.completetask());
    String expectedMessage = "Exception occurred while making changes";
    String actualMessage = exception.getMessage();
    Assertions.assetTrue(actualMessage.contains(expectedMessage));
}

I am getting an error for this test case - the check exception is invalid for this method Invalid java.lang.Exception : Error

Can I know what wrong I am doing here ?

Can you share more details about the error? For example the stack trace could be helpful. — yaken, Apr 30 '22 at 21:42
This the only error i am getting, Is there any other way to test this scenario — NewDBLearner, Apr 30 '22 at 21:46
There is no exception thrown from the method `completeTask` as it is caught and only logged — Bahij.Mik, Apr 30 '22 at 22:03
did you try throwing new Exception inside catch statement and add method signature with throws Excepetion or custom exception ? — sk1030, May 01 '22 at 07:23
The answer [here](https://stackoverflow.com/a/40268447/10343888) helps you. — fatih, May 01 '22 at 20:48

OscarRyz · Answer 1 · 2022-05-01T21:39:22.597

You are expecting your method to thrown an exception but in your code, you're handling and logging the exception and no exception is thrown:

public void completetask(){
   try {
     RemoteUser rm = usrRepo.findById(12);
     assistenRepo.save(rm); // <-- Exception is thrown... 
   } catch(Exception e){ // <-- Catched here
    log.error("Exception occurred while making changes {}", e,getMessage());
   }
   // <-- Method finishes normally. 
}

You should be seeing the following in the output:

Exception occurred while making changes Error Abnormal

But your test will be failing here:

   Exception exception = Assestions.assertThrow(Exception.class, () -> usrService.completetask());

Because the exception was never thrown. If you comment out the exception handling try / catch it will pass that point but now it will fail comparing the error messages.

EDIT:

I know this scenario but the problem here is how to solve this issue? How can we write test scenario for this condition –

If you want to verify your exception was handled just remove verification:

@Test
public void completetaskTest(){
    RemoteUser rm = getDummyRemoteUsr();
    when(usrRepo.findById(12)).thenReturn(rm);
    when(assistenRepo.save(rm)).thenThrow(new Exception("Error Abnormal"));
    assertTrue(true); // if we reached this line, in means the error has handled. 

}

If you really want to go further and check if the message matches (which it might be overkill) you can check the logger, but again, I would't recommend it.

Something like this:

@Auto
Logger log;

...
@Test
public void completetaskTest(){
    RemoteUser rm = getDummyRemoteUsr();
    when(usrRepo.findById(12)).thenReturn(rm);
    when(assistenRepo.save(rm)).thenThrow(new Exception("Error Abnormal"));
   
    // Verify the `log.error` was invoked with exactly those parameters
    verify(log, times(1)).error("Exception occurred while making changes {}", "Error Abnormal");

}

That means the exception was thrown, cached and the logger was invoked.

I know this scenario but the problem here is how to solve this issue? How can we write test scenario for this condition — NewDBLearner, May 01 '22 at 20:36
```org.mockitio.exceptions.base.MockitoException. Checked Exception is invalid for this method. Invalid java.lang.exception: Error Abnormal``` No its not working — NewDBLearner, May 03 '22 at 06:14
Figure out what kind of exceptions do the `save` method throws and then use that in the `thenThrow` call. It seems the problem is you're instrumenting the `when/thenThrow` with an exception that `save` cannot throw in the first place, hence the error. Then the rest of the answer above still applies. — OscarRyz, May 03 '22 at 18:31
Most likely `save` doesn't throw a checked exception (like `java.lang.Exception`) and it might fail somehow else. Try throwing a `RuntimeException` just to verify, but definitely you'll be better off if you handle something that can actually happen — OscarRyz, May 03 '22 at 18:34

score 1 · Answer 2 · answered May 01 '22 at 21:22

You are not throwing your error, you are just writing a log with one log line.

catch(Exception e){
   log.error("Exception occurred while making changes {}", e,getMessage());
}

Here is the javadoc on Assertions.assertThrows:

Assert that execution of the supplied executable throws an exception of the expectedType and return the exception. If no exception is thrown, or if an exception of a different type is thrown, this method will fail. If you do not want to perform additional checks on the exception instance, ignore the return value.

That's why your assertThrows method will fail under all circumstances.

So either throw an error in your method you want to test, or check the log print in exceptions for testing.

How to test exception scenario in junit 5 in spring boot?

2 Answers2