diff --git a/core-java-8/src/main/java/com/baeldung/convertlisttomap/ConvertListToMapService.java b/core-java-8/src/main/java/com/baeldung/convertlisttomap/ConvertListToMapService.java
index 679e753c56..88fc175f38 100644
--- a/core-java-8/src/main/java/com/baeldung/convertlisttomap/ConvertListToMapService.java
+++ b/core-java-8/src/main/java/com/baeldung/convertlisttomap/ConvertListToMapService.java
@@ -5,14 +5,15 @@ import java.util.List;
 import java.util.Map;
 import java.util.stream.Collectors;
 
-import org.apache.commons.collections4.IterableUtils;
 import org.apache.commons.collections4.MapUtils;
 import com.google.common.collect.Maps;
 
 public class ConvertListToMapService {
 
     public Map<Integer, Animal> convertListBeforeJava8(List<Animal> list) {
-        Map<Integer, Animal> map = new HashMap<Integer, Animal>();
+
+        Map<Integer, Animal> map = new HashMap<>();
+
         for (Animal animal : list) {
             map.put(animal.getId(), animal);
         }
@@ -30,20 +31,9 @@ public class ConvertListToMapService {
         return map;
     }
 
-    public Map<Integer, Animal> convertListWithApacheCommons1(List<Animal> list) {
+    public Map<Integer, Animal> convertListWithApacheCommons(List<Animal> list) {
 
-        Map<Integer, Animal> map = new HashMap<Integer, Animal>();
-
-        IterableUtils.forEach(list, animal -> {
-            map.put(animal.getId(), animal);
-        });
-
-        return map;
-    }
-
-    public Map<Integer, Animal> convertListWithApacheCommons2(List<Animal> list) {
-
-        Map<Integer, Animal> map = new HashMap<Integer, Animal>();
+        Map<Integer, Animal> map = new HashMap<>();
 
         MapUtils.populateMap(map, list, Animal::getId);
 
diff --git a/core-java-8/src/test/java/com/baeldung/convertlisttomap/ConvertListToMapServiceUnitTest.java b/core-java-8/src/test/java/com/baeldung/convertlisttomap/ConvertListToMapServiceUnitTest.java
index 4e78af08cd..a4234d2af4 100644
--- a/core-java-8/src/test/java/com/baeldung/convertlisttomap/ConvertListToMapServiceUnitTest.java
+++ b/core-java-8/src/test/java/com/baeldung/convertlisttomap/ConvertListToMapServiceUnitTest.java
@@ -29,6 +29,7 @@ public class ConvertListToMapServiceUnitTest {
         list.add(cow);
         Animal goat = new Animal(5, "Goat");
         list.add(goat);
+
     }
 
     @Test
@@ -56,18 +57,11 @@ public class ConvertListToMapServiceUnitTest {
     }
 
     @Test
-    public void givenAList_whenConvertWithApacheCommons1_thenReturnMapWithTheSameElements() {
+    public void givenAList_whenConvertWithApacheCommons_thenReturnMapWithTheSameElements() {
 
-        Map<Integer, Animal> map = convertListService.convertListWithApacheCommons1(list);
+        Map<Integer, Animal> map = convertListService.convertListWithApacheCommons(list);
 
         assertThat(map.values(), containsInAnyOrder(list.toArray()));
     }
 
-    @Test
-    public void givenAList_whenConvertWithApacheCommons2_thenReturnMapWithTheSameElements() {
-
-        Map<Integer, Animal> map = convertListService.convertListWithApacheCommons2(list);
-
-        assertThat(map.values(), containsInAnyOrder(list.toArray()));
-    }
 }
diff --git a/core-java-8/src/test/java/com/baeldung/convertlisttomap/ConvertListWithDiplicatedIdToMapServiceUnitTest.java b/core-java-8/src/test/java/com/baeldung/convertlisttomap/ConvertListWithDiplicatedIdToMapServiceUnitTest.java
new file mode 100644
index 0000000000..6d3ad9e76e
--- /dev/null
+++ b/core-java-8/src/test/java/com/baeldung/convertlisttomap/ConvertListWithDiplicatedIdToMapServiceUnitTest.java
@@ -0,0 +1,68 @@
+package com.baeldung.convertlisttomap;
+
+import static org.hamcrest.MatcherAssert.assertThat;
+import static org.hamcrest.Matchers.hasItem;
+import static org.hamcrest.Matchers.hasSize;
+
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Map;
+
+import org.junit.Before;
+import org.junit.Test;
+
+public class ConvertListWithDiplicatedIdToMapServiceUnitTest {
+    List<Animal> duplicatedIdList;
+
+    private ConvertListToMapService convertListService = new ConvertListToMapService();
+
+    @Before
+    public void init() {
+
+        this.duplicatedIdList = new ArrayList<>();
+
+        Animal cat = new Animal(1, "Cat");
+        duplicatedIdList.add(cat);
+        Animal dog = new Animal(2, "Dog");
+        duplicatedIdList.add(dog);
+        Animal pig = new Animal(3, "Pig");
+        duplicatedIdList.add(pig);
+        Animal cow = new Animal(4, "Cow");
+        duplicatedIdList.add(cow);
+        Animal goat = new Animal(4, "Goat");
+        duplicatedIdList.add(goat);
+
+    }
+
+    @Test
+    public void givenADupIdList_whenConvertBeforeJava8_thenReturnMapWithRewrittenElement() {
+
+        Map<Integer, Animal> map = convertListService.convertListBeforeJava8(duplicatedIdList);
+
+        assertThat(map.values(), hasSize(4));
+        assertThat(map.values(), hasItem(duplicatedIdList.get(4)));
+    }
+
+    @Test
+    public void givenADupIdList_whenConvertWithApacheCommons_thenReturnMapWithRewrittenElement() {
+
+        Map<Integer, Animal> map = convertListService.convertListWithApacheCommons(duplicatedIdList);
+
+        assertThat(map.values(), hasSize(4));
+        assertThat(map.values(), hasItem(duplicatedIdList.get(4)));
+    }
+
+    @Test(expected = IllegalStateException.class)
+    public void givenADupIdList_whenConvertAfterJava8_thenException() {
+
+        convertListService.convertListAfterJava8(duplicatedIdList);
+    }
+
+    @Test(expected = IllegalArgumentException.class)
+    public void givenADupIdList_whenConvertWithGuava_thenException() {
+
+        convertListService.convertListWithGuava(duplicatedIdList);
+
+    }
+
+}