Map equality using Hamcrest

Question

I'd like to use hamcrest to assert that two maps are equal, i.e. they have the same set of keys pointing to the same values.

My current best guess is:

assertThat( affA.entrySet(), hasItems( affB.entrySet() ); 

which gives:

The method assertThat(T, Matcher<T>) in the type Assert is not applicable for the arguments (Set<Map.Entry<Householdtypes,Double>>, Matcher<Iterable<Set<Map.Entry<Householdtypes,Double>>>>)

I've also looked into variations of containsAll, and some others provided by the hamcrest packages. Can anyone point me in the right direction? Or do I have to write a custom matcher?

Answer 1

The shortest way I've come up with is two statements:

assertThat( affA.entrySet(), everyItem(isIn(affB.entrySet()))); assertThat( affB.entrySet(), everyItem(isIn(affA.entrySet()))); 

But you can probably also do:

assertThat(affA.entrySet(), equalTo(affB.entrySet())); 

depending on the implementations of the maps, and sacrificing the clarity of the difference report: that would just tell you that there is a difference, while the statement above would also tell you which one.

UPDATE: actually there is one statement that works independently of the collection types:

assertThat(affA.entrySet(), both(everyItem(isIn(affB.entrySet()))).and(containsInAnyOrder(affB.entrySet()))); 

Answer 2

Sometimes Map.equals() is enough. But sometimes you don't know the types of Maps is returned by code under tests, so you don't know if .equals() will properly compare that map of unknown type returned by code with map constructed by you. Or you don't want to bind your code with such tests.

Additionally, constructing a map separately to compare the result with it is IMHO not very elegant:

Map<MyKey, MyValue> actual = methodUnderTest();  Map<MyKey, MyValue> expected = new HashMap<MyKey, MyValue>(); expected.put(new MyKey(1), new MyValue(10)); expected.put(new MyKey(2), new MyValue(20)); expected.put(new MyKey(3), new MyValue(30)); assertThat(actual, equalTo(expected)); 

I prefer using machers:

import static org.hamcrest.Matchers.hasEntry;  Map<MyKey, MyValue> actual = methodUnderTest(); assertThat(actual, allOf(                       hasSize(3), // make sure there are no extra key/value pairs in map                       hasEntry(new MyKey(1), new MyValue(10)),                       hasEntry(new MyKey(2), new MyValue(20)),                       hasEntry(new MyKey(3), new MyValue(30)) )); 

I have to define hasSize() myself:

public static <K, V> Matcher<Map<K, V>> hasSize(final int size) {     return new TypeSafeMatcher<Map<K, V>>() {         @Override         public boolean matchesSafely(Map<K, V> kvMap) {             return kvMap.size() == size;         }          @Override         public void describeTo(Description description) {             description.appendText(" has ").appendValue(size).appendText(" key/value pairs");         }     }; } 

And there is another variant of hasEntry() that takes matchers as parameters instead of exact values of key and value. This can be useful in case you need something other than equality testing of every key and value.