Hamcrest ArrayList matcher

Question

I am trying to use a mock and check that the argument passed into the mock is the correct ArrayList<MyModel>. I have defined the boolean equals method on MyModel, but I can't find the right matcher that uses the equals method. The matchers I have been writing only compare the object_id's which are obviously different. My test looks something like so:

MainActivity activity = mock(MainActivity.class);
MyRequest subject = new MyRequest(activity);
ArrrayList<MyModel> list = ...;
subject.makeRequest();
verify(activity).handleSuccess(argThat(is(list)));

Does anyone know a matcher that will use the boolean equal on MyModel?

Why this doesn't work for you? `verify(activity).handleSuccess(argThat(equalTo(expected)));` — aim, Aug 02 '13 at 19:03
@aim it compares the object_id's and since the argument that is called is a different instance of `ArrayList` the equality comparison returns false. — trev9065, Aug 02 '13 at 19:55
Hmm.. I thought `equalTo` invoke equal on `ArrayList` and then it applies on each element of list (like this `java.util.AbstractList#equals`)... — aim, Aug 02 '13 at 20:00
@aim I thought the same, but it is giving me the same error. — trev9065, Aug 02 '13 at 21:32
Check [this](https://gist.github.com/funster/6143998) out (it's not android classes but it just simple idea), if you run it prints: `Equals invoked: MyModel{id=1} Equals invoked: MyModel{id=1}`. So `equalTo` compared base on `equals` method, but not reference (or object_id's) — aim, Aug 02 '13 at 22:31
Post the failure message for clarity. The `equalTo` matcher indeed uses the object's built-in `equals` method. Note that `ArrayList`'s method requires the elements to be in the same order in both lists. — David Harkness, Aug 04 '13 at 23:39

score 0 · Answer 1 · edited May 23 '17 at 12:32

According to the Hamcrest tutorial, you can use any of the following to compare using Object.equals:

argThat(is(list))
argThat(is(equalTo(list))
argThat(equalTo(list))

Furthermore, List.equals(Object) is specifically defined to compare e1.equals(e2) for every element e1 and e2 in corresponding positions in the list.

Double-check that you've fulfilled everything you need to do to properly override equals:

Does your MyModel.equals method receive an Object parameter instead of a MyModel? If the parameter is any type other than Object, it isn't a proper override and won't work.
Is MyModel.equals reflective, symmetric, transitive, and consistent? It's unlikely that your equals would fail in the other direction, but there's no guarantee on which object the equals method will be called.
When two objects are equal, do their hashCode values return equal integers? Collection implementations are free to check hash code equality as a "shortcut" before checking object-to-object equality.

To check those points, you may want to write a test to specifically for equals. I recommend Guava's EqualsTester, which checks most of these properties automatically for you.

Hamcrest ArrayList matcher

1 Answers1