[FIXED] JUnit - compare unknown Collection and ArrayList

Issue

I want to compare Collection (products) (in my case it is LinkedHashMap$LinkedValues) and ArrayList.

The test

assertThat(products, equalTo(Lists.newArrayList(product1, product2, product3)));

doesn't work because LinkedValues doesn't implement equals method. So I changed my test to:

  assertThat(new ArrayList<>(products), equalTo(Lists.newArrayList(product1, product2, product3)));

Is there a better solution where I do not have to check if the collection implements equals method?

Solution

Since you're using Hamcrest, you should use the slightly confusingly named method Matchers.contains(). It checks whether the target collection contains the same elements in the same order as the original collection.

Given

Map<String, String> linkedHashMap = new LinkedHashMap<>();
linkedHashMap.put("a", "A");
linkedHashMap.put("b", "B");

This will pass:

assertThat(linkedHashMap.values(), contains("A", "B"));

and this would fail:

assertThat(linkedHashMap.values(), contains("B", "A"));

---

Note that Hamcrest has been long dead and even though it works fine and is okay for 99% of usages, you will be shocked by how good AssertJ is, how much functionality it provides and how easy asserting can be.

With AssertJ:

assertThat(linkedHashMap.values()).containsExactly("A", "B");

Answered By - Petr Janeček