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:

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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

Another option available now is to use the Cirneco extension for Hamcrest. It has hasSameKeySet() (as well as other matchers for Guava "collections"). According to your example, it will be:

assertThat(affA, hasSameKeySet(affB));

You can use the following dependency for a JDK7-based project:

<dependency>
  <groupId>it.ozimov</groupId>
  <artifactId>java7-hamcrest-matchers</artifactId>
  <version>0.7.0</version>
</dependency>

or the following if you are using JDK8 or superior:

<dependency>
  <groupId>it.ozimov</groupId>
  <artifactId>java8-hamcrest-matchers</artifactId>
  <version>0.7.0</version>
</dependency>

Answer 3

If you need to compare a set of results with expectations and if you choose to use assertj library, you can do this:

// put set of expected values by your test keys
Map<K, V> expectations = ...;

// for each test key get result
Map<K, V> results = expectations.keySet().stream().collect(toMap(k -> k, k -> getYourProductionResult(k)));

assertThat(results).containsAllEntriesOf(expectations);

Note that containsAllEntriesOf does not compare maps for equality. If your production code returns actually a Map<K, V> you may want to add a check for keys assertThat(results).containsOnlyKeys((K[]) expectations.keySet().toArray());

Answer 4

I favor using Guava ImmutableMap. They support Map.equals() and are easy to construct. The only trick is to explicitly specify type parameters, since hamcrest will assume the ImmutableMap type.

assertThat( actualValue,
            Matchers.<Map<String, String>>equalTo( ImmutableMap.of(
                "key1", "value",
                "key2", "other-value"
) ) );

Answer 5

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.

Answer 6

This works like a charm and doesn't require two assertions like the accepted answer.

assertThat( actualData.entrySet().toArray(), 
    arrayContainingInAnyOrder(expectedData.entrySet().toArray()) );