How to verify Map size using Hamcrest

Question

Map<Integer, Map<String, String>> mapMap = new HashMap<Integer,Map<String, String>>(); 

Currently asserting like this

assertThat(mapMap.size(), is(equalTo(1))); Or assertThat(mapMap.values(), hasSize(1)); 

Are there any other methods like one used with Lists.

assertThat(someListReferenceVariable, hasSize(1));

Answer 1

The good news

There is a matcher that does exactly what you want in the current master branch of the JavaHamcrest project. You can call it like so:

assertThat(mapMap, aMapWithSize(1)); 

And the bad news

Unfortunately this matcher is not in the latest release of Hamcrest (1.3).

[Update] And finally the very good news

The aforementioned matcher is included in the newly released version 2.1.

Answer 2

There is none in Hamcrest 1.3, but you can very easily create your own:

public class IsMapWithSize<K, V> extends FeatureMatcher<Map<? extends K, ? extends V>, Integer> {     public IsMapWithSize(Matcher<? super Integer> sizeMatcher) {         super(sizeMatcher, "a map with size", "map size");     }      @Override     protected Integer featureValueOf(Map<? extends K, ? extends V> actual) {         return actual.size();     }      /**      * Creates a matcher for {@link java.util.Map}s that matches when the      * <code>size()</code> method returns a value that satisfies the specified      * matcher.      * <p/>      * For example:      *       * <pre>      * Map&lt;String, Integer&gt; map = new HashMap&lt;&gt;();      * map.put(&quot;key&quot;, 1);      * assertThat(map, isMapWithSize(equalTo(1)));      * </pre>      *       * @param sizeMatcher      *            a matcher for the size of an examined {@link java.util.Map}      */     @Factory     public static <K, V> Matcher<Map<? extends K, ? extends V>> isMapWithSize(Matcher<? super Integer> sizeMatcher) {         return new IsMapWithSize<K, V>(sizeMatcher);     }      /**      * Creates a matcher for {@link java.util.Map}s that matches when the      * <code>size()</code> method returns a value equal to the specified      * <code>size</code>.      * <p/>      * For example:      *       * <pre>      * Map&lt;String, Integer&gt; map = new HashMap&lt;&gt;();      * map.put(&quot;key&quot;, 1);      * assertThat(map, isMapWithSize(1));      * </pre>      *       * @param size      *            the expected size of an examined {@link java.util.Map}      */     @Factory     public static <K, V> Matcher<Map<? extends K, ? extends V>> isMapWithSize(int size) {         Matcher<? super Integer> matcher = equalTo(size);         return IsMapWithSize.<K, V> isMapWithSize(matcher);     }  } 

Testing:

    Map<String, Integer> map = new HashMap<>();     map.put("key", 1);     assertThat(map, isMapWithSize(1));     assertThat(map, isMapWithSize(equalTo(1)));