如何知道什么导致assertEquals方法在单元测试中失败？

Question

I am missing good failure messages when using assertEquals() on objects or collections. When it fails, the error message prints out the expected object and the actual object using toString() method. It does not print out exactly what causes the inequality. Certainly when comparing two collections, the message that comes with the AssertionError is kind of useless or time consuming to figure out what is wrong.

Here are two possible solutions that I don't want to use:

1. It's an option to write very specific assertions , but that is too time consuming.
2. It's also an option to use logging inside the equals methods of your domain. If equals() returns false, it also prints out the attribute that causes the failure. I only need to look at my console and see the printed message right before the AssertionError. For collections on the other hand, the equals of the collection is used. If for example the lists are not equal because 1 specific object is only present in one of the lists, I would also want that specific log message to appear in the console. But I don't want to write that code myself .

Are there frameworks that have this kind of logging when using equals?

Are there best practices to handle this problem (or to avoid it in the first place that you don't need this kind of logging)?

Answer 1

The Spock framework provides this kind of feature. You can use any expression as assertion and it will print exactly why it failed:

assert stack.size() == 2  // this is your assertEquals

And you get:

Condition not satisfied:

stack.size() == 2
|     |      |
|     1      false
[push me]

We have switched to Spock in place of JUnit in all our projects now because it's so convenient.