AssertJ provides dedicated assertions for Map types, covering key presence, value correctness, full entry matching, and size checks. When assertThat() receives a Map, it returns a MapAssert with all these methods available.

entry() helper

The static entry(key, value) method from Assertions creates a Map.Entry for use in assertions, making it easy to check exact key-value pairs without constructing entries manually.

Key Map Assertion Methods

containsKey, doesNotContainKey, containsValue, containsEntry, contains (with entry()), hasSize, isEmpty.

Example

package com.logicbig.example;

import org.junit.jupiter.api.Test;

import java.util.Map;
import static org.assertj.core.api.Assertions.*;

public class MapAssertionsExample {

    @Test
    void myTest() {
        Map<String, Integer> scores = Map.of("Alice",
                                             95,
                                             "Bob",
                                             80,
                                             "Charlie",
                                             70);

        // key checks
        assertThat(scores).containsKey("Alice")
                          .doesNotContainKey("Dave");
        System.out.println("Key checks passed");

        // value checks
        assertThat(scores).containsValue(95)
                          .doesNotContainValue(100);
        System.out.println("Value checks passed");

        // exact entry
        assertThat(scores).containsEntry("Bob", 80);
        System.out.println("Entry check passed");

        // using entry() helper
        assertThat(scores).contains(entry("Alice", 95), entry("Charlie", 70));
        System.out.println("entry() helper check passed");

        // size
        assertThat(scores).hasSize(3);
        System.out.println("Size check passed");
    }
}

Output

$ mvn clean test -Dtest=*
[INFO] Scanning for projects...
[INFO] 
[INFO] ------------< com.logicbig.example:assertj-map-assertions >-------------
[INFO] Building assertj-map-assertions 1.0-SNAPSHOT
[INFO]   from pom.xml
[INFO] --------------------------------[ jar ]---------------------------------
[INFO] 
[INFO] --- clean:3.2.0:clean (default-clean) @ assertj-map-assertions ---
[INFO] 
[INFO] --- resources:3.3.1:resources (default-resources) @ assertj-map-assertions ---
[INFO] skip non existing resourceDirectory D:\example-projects\assertj\assertj-map-assertions\src\main\resources
[INFO] 
[INFO] --- compiler:3.11.0:compile (default-compile) @ assertj-map-assertions ---
[INFO] No sources to compile
[INFO] 
[INFO] --- resources:3.3.1:testResources (default-testResources) @ assertj-map-assertions ---
[INFO] skip non existing resourceDirectory D:\example-projects\assertj\assertj-map-assertions\src\test\resources
[INFO] 
[INFO] --- compiler:3.11.0:testCompile (default-testCompile) @ assertj-map-assertions ---
[INFO] Changes detected - recompiling the module! :source
[INFO] Compiling 1 source file with javac [debug target 17] to target\test-classes
[INFO] 
[INFO] --- surefire:3.2.5:test (default-test) @ assertj-map-assertions ---
[INFO] Using auto detected provider org.apache.maven.surefire.junitplatform.JUnitPlatformProvider
[WARNING] file.encoding cannot be set as system property, use <argLine>-Dfile.encoding=...</argLine> instead
[INFO] 
[INFO] -------------------------------------------------------
[INFO]  T E S T S
[INFO] -------------------------------------------------------
[INFO] Running com.logicbig.example.MapAssertionsExample
Key checks passed
Value checks passed
Entry check passed
entry() helper check passed
Size check passed
[INFO] Tests run: 1, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 0.086 s -- in com.logicbig.example.MapAssertionsExample
[INFO] 
[INFO] Results:
[INFO] 
[INFO] Tests run: 1, Failures: 0, Errors: 0, Skipped: 0
[INFO] 
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------
[INFO] Total time:  2.684 s
[INFO] Finished at: 2026-03-03T13:35:07+08:00
[INFO] ------------------------------------------------------------------------

Conclusion

The output confirms each map assertion passes: key presence, value lookup, exact entry matching using entry(), and absence checks all work as expected. AssertJ's map assertions make it straightforward to validate configuration maps, caches, or any key-value output from your code.

Example Project

Dependencies and Technologies Used:

• assertj-core 3.27.7 (Rich and fluent assertions for testing in Java)
  
• junit-jupiter-engine 6.0.2 (Module "junit-jupiter-engine" of JUnit)
  
• JDK 17
• Maven 3.9.11