Unit Test compareTo / Comparable

[Gregg Bolinger]

This is probably a dumb question but I can't find anything for JUnit or TestNG that allows me to assertCompareble or assertCompareTo or something similar. Furthermore I am not even sure if such things should be tested.

Can someone point me in the right direction?

Thanks.

[Jeanne Boyarsky]

Gregg,
I don't follow what you are asking for. The following checks objects are comparable. I suspect you means something else though.

assertEquals("comparable", 0, obj1.compareTo(obj2));

[Gregg Bolinger]

Originally posted by Jeanne Boyarsky:
Gregg,
I don't follow what you are asking for. The following checks objects are comparable. I suspect you means something else though.

assertEquals("comparable", 0, obj1.compareTo(obj2));

And that's what I was looking for. Thanks.

[Gregg Bolinger]

I was looking at the API. How do you know to put "comparable" in for the message? What are the other message options?

[bart zagers]

Originally posted by Gregg Bolinger:
I was looking at the API. How do you know to put "comparable" in for the message? What are the other message options?

The message is just a reference that is printed when the test fails. There are no special options and it has nothing to do with the actual test.
Or am I misinterpreting the question?

[Gregg Bolinger]

Originally posted by bart zagers:


The message is just a reference that is printed when the test fails. There are no special options and it has nothing to do with the actual test.
Or am I misinterpreting the question?

Nope, works for me. So I was doing..

Assert.assertTrue(obj1.compareTo(obj2) == 0);

Is there any advantage/disadvantage to this over Jeanne's suggestion?

[Lasse Koskela]

Originally posted by Gregg Bolinger:
Assert.assertTrue(obj1.compareTo(obj2) == 0);

Is there any advantage/disadvantage to this over Jeanne's suggestion?

Well, when your assertion fails you only hear "AssertionFailedError". When Jeanne's assertion fails she hears "AssertionFailedError: comparable".

Especially if you're using this assertion more than once, I'd recommend considering a "custom" assertion method such as this:

public static void assertComparable(Object a, Object b) {
    String msg = "Objects were not comparable: <" + a + ">, <" + b + ">";
    assertEquals(msg, 0, a.compareTo(b));
}

[Gregg Bolinger]

Thanks. I'll try that.

[Jeanne Boyarsky]

Originally posted by Lasse Koskela:
When Jeanne's assertion fails she hears "AssertionFailedError: comparable".

Also note that "Jeanne's assertion" uses assertEquals() rather than assertTrue(). This means that I get the actual value in the message. For comapreTo, I can see if it is larger or smaller than the expected 0 which gives me an extra clue before I look to see what went wrong.

Lasse's message is certainly even more descriptive.

[Ilja Preuss]

Note that the tests suggested so far don't really fully test that compareTo is working as expected - for that you needed to test different scenarios.

Take a look at http://junit-addons.sourceforge.net/junitx/extensions/ComparabilityTestCase.html to simplify that task. (You might also want to take a look at the source code to learn how it's done.)

[Jeanne Boyarsky]

Originally posted by Ilja Preuss:
Note that the tests suggested so far don't really fully test that compareTo is working as expected - for that you needed to test different scenarios.

Oh! I thought I wasn't understanding the question. Your explanation of it makes sense as for the real question.