Added the test. (#12947)

core-java-modules/core-java-collections-maps-4/pom.xml

@@ -15,6 +15,11 @@
     </parent>
 
     <dependencies>
+        <dependency>
+            <groupId>jakarta.ws.rs</groupId>
+            <artifactId>jakarta.ws.rs-api</artifactId>
+            <version>3.1.0</version>
+        </dependency>
         <dependency>
             <groupId>org.apache.commons</groupId>
             <artifactId>commons-collections4</artifactId>

core-java-modules/core-java-collections-maps-4/src/test/java/com/baeldung/multivaluedmap/MultivaluedMapUnitTest.java

@@ -0,0 +1,43 @@
+package com.baeldung.multivaluedmap;
+
+import org.junit.jupiter.api.Test;
+
+import java.util.HashMap;
+import java.util.Map;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertNotNull;
+
+// Unit test for MultivaluedMap.
+public class MultivaluedMapUnitTest {
+    
+    // Testing MultivaluedHashMap.
+    @Test
+    public void givenMultivaluedHashMap_whenEquals_thenTrue() {
+        jakarta.ws.rs.core.MultivaluedMap<String, Integer> mulmap = new jakarta.ws.rs.core.MultivaluedHashMap<>();
+
+        // Mapping keys to values.
+        mulmap.addAll("first", 1, 2, 3);
+        mulmap.add(null, null);
+
+        assertNotNull(mulmap, "The MultivaluedHashMap is null!");
+        assertEquals(1, mulmap.getFirst("first"), "The key isn't mapped to the right values!");
+        assertEquals(null, mulmap.getFirst(null), "MultivaluedHashMap didn't accept null!");
+    }
+
+    // Testing HashMap.
+    @Test
+    public void givenHashMap_whenEquals_thenTrue() {
+        Map<String, Integer> map = new HashMap<>();
+
+        // Putting key-value pairs into our map.
+        map.put("first", 1);
+        map.put(null, 2);
+        map.put("third", null);
+
+        assertNotNull(map, "The HashMap is null!");
+        assertEquals(1, map.get("first"), "The key isn't mapped to the right value!");
+        assertEquals(2, map.get(null), "HashMap didn't accept null as key!");
+        assertEquals(null, map.get("third"), "HashMap didn't accept null value!");
+    }
+}