Should I use try-catch block with Assertions

Question

This question is in mind for quite a long time and I want to know whether should I use try-catch Block with assertion or not? for example-

1. assertEquals(actual, expected); 2. try { assertEquals(actual, expected); } catch(AssertionError e) { e.printStackTrace(); }

What is the good practice? 1 or 2? TIA

What benefit is there in catching the exception? Surely you want the test to fail... — Jon Skeet
– Jon Skeet, Commented Sep 27, 2016 at 8:16
@JonSkeet and what if the purpose of "catching" failed assertions is to send them to the back-end server? This can help to inform the developer in order to fix them — user2342558
– user2342558, Commented Feb 9 at 11:05
@JonSkeet why did you say "dependency on a unit test framework"? I only use try-catch, without any dependency on a test framework. Sure I don't bring testing framework on client in prod env. — user2342558
– user2342558, Commented Feb 10 at 8:52
@JonSkeet thanks, yes, I didn't know that assertEquals belong to a unit test framework. So I'll delete my comments for clean purpose — user2342558
– user2342558, Commented Feb 10 at 9:57

Eduardo Yáñez Parareda · Accepted Answer · 2016-09-27 08:33:38Z

No, for sure you shouldn't do that. The purpose of the assertion is that when it fails, it throws the assertion error so the test unit engine is notified of that.

So, simply, do the assert. And make it working :). If it fails, you should solve the problem.

On the other hand, if what you want to test if that an exception is thrown. You can do it in several ways:

@Test(expected = NullPointerException.class) public void myTestForException() { callMethodThatThrowsNullPointerException(); }

or you can use a try/catch:

@Test public void myTest() { try { fail("Should throw whatever"); } catch (MyException e) { // Everything is fine, test passed } }

There's a better way of testing that exceptions are thrown. Use the JUnit ExpectedException rules. They're documented on the JUnit web site.

Dawood ibn Kareem · Accepted Answer · 2016-09-27 09:26:25Z

The whole point of using JUnit, or TestNG, or something of that kind for your tests is that you can have thousands of tests in your project, and automate the testing. Running the tests can be part of the build process, and you get some feedback as to how many of the tests have passed. This is absolutely essential when your project consists of more than just a small handful of classes.

Your idea about catching the error that assertEquals throws and reporting it to the console is not a good one. Primarily because it makes the test pass when the assertion fails. That means that whatever you're using to run your tests (for example, Jenkins) is reporting the wrong result. You'll see, for example, that 5000 out of 5000 tests pass, even if a whole lot of them contain assertions that fail. And suddenly your large suite of tests has very little value.

Moreover, that stack trace that you so carefully print is going to get lost, in a flood of output from all the various tests.

So the short answer is that your idea (1) is the correct thing to do. It's what everyone does. And it means that the results of your tests are reported appropriately. You should never write tests like your idea (2).

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