JUnit – How to test a Map

By mkyong | Updated: June 12, 2016

Viewed: 17,883 (+67 pv/w)

Tags: hamcrest junit map

Forget about JUnit assertEquals(), to test a Map, uses the more expressive IsMapContaining class from hamcrest-library.jar

	<dependencies>
		<dependency>
			<groupId>junit</groupId>
			<artifactId>junit</artifactId>
			<version>4.12</version>
			<scope>test</scope>
			<exclusions>
				<exclusion>
					<groupId>org.hamcrest</groupId>
					<artifactId>hamcrest-core</artifactId>
				</exclusion>
			</exclusions>
		</dependency>
		<!-- This will get hamcrest-core automatically -->
		<dependency>
			<groupId>org.hamcrest</groupId>
			<artifactId>hamcrest-library</artifactId>
			<version>1.3</version>
			<scope>test</scope>
		</dependency>
	</dependencies>

1. IsMapContaining Examples

All the below assertThat checks will be passed.

package com.mkyong;

import org.hamcrest.collection.IsMapContaining;
import org.junit.Test;

import java.util.HashMap;
import java.util.Map;

import static org.hamcrest.CoreMatchers.is;
import static org.hamcrest.CoreMatchers.not;
import static org.hamcrest.MatcherAssert.assertThat;

public class MapTest {

    @Test
    public void testAssertMap() {

        Map<String, String> map = new HashMap<>();
        map.put("j", "java");
        map.put("c", "c++");
        map.put("p", "python");
        map.put("n", "node");

        Map<String, String> expected = new HashMap<>();
        expected.put("n", "node");
        expected.put("c", "c++");
        expected.put("j", "java");
        expected.put("p", "python");

        //All passed / true

        //1. Test equal, ignore order
        assertThat(map, is(expected));

        //2. Test size
        assertThat(map.size(), is(4));

        //3. Test map entry, best!
        assertThat(map, IsMapContaining.hasEntry("n", "node"));

        assertThat(map, not(IsMapContaining.hasEntry("r", "ruby")));

        //4. Test map key
        assertThat(map, IsMapContaining.hasKey("j"));

        //5. Test map value
        assertThat(map, IsMapContaining.hasValue("node"));

    }

}

References

1. Hamcrest official site
2. IsMapContaining JavaDoc
3. JUnit – How to test a List