More hamcrest collections goodness

I have been using Hamcrest more in my unit tests. JUnit 4.11 included only a portion of the matchers available in Hamcrest 1.3. (The ones packaged in hamcrest-core specifically). To include other useful matchers from Hamcrest, add the following to the maven pom.xml


I found the collections one very handy. For example, to test the size of a list:

import static org.hamcrest.collection.IsCollectionWithSize.hasSize;
import static org.junit.Assert.assertThat;
List list = new ArrayList();
assertThat(list, hasSize(0));

JUnit 4.11 and its new Matchers

I have never used the Hamcrest matchers with JUnit before. Not until last week. I noticed in the release note that JUnit 4.11 included Hamcrest 1.3, with its Matchers and improved assertThat syntax. Reading the examples on the release note, I was intrigued.

To use the new Matchers and assertThat, you need to include the following imports

import static org.junit.Assert.*;
import static org.hamcrest.CoreMatchers.*;
Number Objects

The first improvement I noticed were comparison with Java number objects.

Long l = new Long(10);
assertEquals(10L, l);
assertThat(l, is(10L));

With the old assertEquals, the compiler would complain about The method assertEquals(Object, Object) is ambiguous for type X. You need to change both parameters to either long values or Long objects for the assert to work, for example

assertEquals(10L, l.longValue());

On the other hand, assertThat and the is() matcher works just fine.


I saw a few very handy looking matchers for Collections from looking at the CoreMatchers javadoc. For example, hasItem, hasItems, everyItem. I had the opportunity to use hasItems in my unit tests last week to check if a List object contains items from a given list of values. It was as simple to use as this

assertThat(list, hasItems("apples", "oranges"));

I’m a fan of this new way of matching things in JUnit.