Will an assertion error be caught by in a catch block for java exception?

Question

Code:-

try {
    Assert.assertEquals("1", "2");
} catch (Exception e) {
    System.out.println("I am in error block");
}

If the assert statements fails, I would like to capture the error in the catch block. I am trying with the above code and its not happening.

Will the assertion error be caught by in a catch block for java exception?

Solution 1

You have almost answered your own question. Your catch block will not catch the AssertionError that the Assert throws if it fails, because it is an Error (or, more specifically, it extends java.lang.Error). See the docs for more information on this. Your catch block only catches Throwable objects that extend java.lang.Exception

If you really want to catch it - you need to use

catch (AssertionError e) {
...

However, as others have mentioned, this is a very unusual way to use assertions - they should usually pass and if they fail it is very unusual for you to want to carry on program execution. That's why the failure throws an Error rather than an Exception. You can read more about (not) catching Error in this question.

Are you sure you don't just want a test - if ( variableName == "1")?

NB if you are testing unit-test helper code, like a matcher, it might make sense to catch the AssertionError.

Solution 2

If you want to catch both Exception and Error instances use:

...
catch (Throwable t)
{
...
}

Since both Exception and Error extend Throwable.

Solution 3

Well, I believe you are using JUnit for writing your tests. In that case, you should not catch your Assert.assertEquals() because they should pass for normal test execution. If it throws any exception, it means that your code is not performing as it should.

Comments

[Galet]

yes my assert code throws an exception. But i want to capture all errors such assertions or any other error by Exception class. How can i do it ?

[Aakash]

You can't. AssertionError inherits from Error which means try...catch won't be able to handle them. See here docs.oracle.com/javase/7/docs/api/java/lang/AssertionError.h‌​tml. If you anyways need to catch them, see SpaceCowboy's answer.

[gkephorus]

When one wants to see if a unit-test helper-class is doing the right thing (by unit-testing it ;-) ) one would expect to be able to catch such a AssertionError. That would be a valid situation to catch it, wouldn't it?

[J Richard Snape]

@gkephorus yes, I suppose it could be. Feel free to edit that in as an "N.B." if you like and I'll approve it :)

[MasterJoe]

@JRichardSnape - I want to compare two java objects (obtained from json objects) which have only string variables with getters & setters i.e. POJO. I only want to compare some (not all) of the variables to determine a match. For one of the variables, only partial value should be compared. Is it a good idea to put all of my asserts into a try catch(AssertionError) block ? That way, I can return false in the catch part to indicate which field mismatched, with a useful error message string. This way, I won't have to write several if else. Sounds ok ?

[danyamachine]

@Aakash that's incorrect - this works fine: try { throw new AssertionError(); } catch( AssertionError e){ System.out.println("ok");}

[josle]

With respect to: "NB if you are testing unit-test helper code, like a matcher, it might make sense to catch the AssertionError" - I would recommend using org.junit.rules.ExpectedException.handleAssertionErrors()

[Aakash]

@danyamachine as I said, we should not catch AssertionError or any Error for that matter. Errors are there to tell developer that something wrong has happened and program should not continue. It's a late reply, but better late than never :)

[truthadjustr]

catch (AssertionError e) { } is not invoked in my case. Thou shall not catch AssertionError is the mantra here.

[JohnK]

This worked for me. Thanks!