Hamcrest Collections Cookbook
Last updated: July 29, 2020
1. Introduction
This cookbook illustrates how to make use of Hamcrest matchers to work with and test collections.
The format of the cookbook is example focused and practical – no extraneous details and explanations necessary.
First, let’s do a quick static import to cover most of the utility APIs we’re going to use next:
import static org.hamcrest.Matchers.*;Further reading:
Hamcrest Common Core Matchers
Explore the different methods of CoreMatchers class in the Hamcrest library.
Hamcrest Bean Matchers
Learn about Hamcrest bean matchers - a tool that provides an effective way of making assertions, a frequently used feature when writing unit tests.
Testing with Hamcrest
In this very practical tutorial, we focus on using the Hamcrest API and on writing neater and more intuitive unit tests for our software.
2. The Cookbook
check if single element is in a collection
List<String> collection = Lists.newArrayList("ab", "cd", "ef");
assertThat(collection, hasItem("cd"));
assertThat(collection, not(hasItem("zz")));check if multiple elements are in a collection
List<String> collection = Lists.newArrayList("ab", "cd", "ef");
assertThat(collection, hasItems("cd", "ef"));check all elements in a collection
– with strict order
List<String> collection = Lists.newArrayList("ab", "cd", "ef");
assertThat(collection, contains("ab", "cd", "ef"));– with any order
List<String> collection = Lists.newArrayList("ab", "cd", "ef");
assertThat(collection, containsInAnyOrder("cd", "ab", "ef"));check if collection is empty
List<String> collection = Lists.newArrayList();
assertThat(collection, empty());check if array is empty
String[] array = new String[] { "ab" };
assertThat(array, not(emptyArray()));check if Map is empty
Map<String, String> collection = Maps.newHashMap();
assertThat(collection, equalTo(Collections.EMPTY_MAP));check if Iterable is empty
Iterable<String> collection = Lists.newArrayList();
assertThat(collection, emptyIterable());check size of a collection
List<String> collection = Lists.newArrayList("ab", "cd", "ef");
assertThat(collection, hasSize(3));checking size of an iterable
Iterable<String> collection = Lists.newArrayList("ab", "cd", "ef");
assertThat(collection, Matchers.<String> iterableWithSize(3));check condition on every item
List<Integer> collection = Lists.newArrayList(15, 20, 25, 30);
assertThat(collection, everyItem(greaterThan(10)));3. Conclusion
This format is an experiment – I’m publishing some of my internal development cookbooks on a given topic – Google Guava and now Hamcrest. The goal is to have this information readily available online – and to add to it whenever I run into a new useful example.
The implementation of all these examples and code snippets can be found over on GitHub – this is a Maven-based project, so it should be easy to import and run as it is.
