From 2aa4e807c0a5bc42997681537009cb02be178f36 Mon Sep 17 00:00:00 2001
From: cror <37755757+cror@users.noreply.github.com>
Date: Thu, 7 Feb 2019 01:57:56 +0100
Subject: [PATCH] toSet, toMap: adding examples with duplicates (#6264)

* BAEL-2548 fix typo

* BAEL-2548 toSet, toMap: added tests with duplicate elements
---
 .../collectors/Java8CollectorsUnitTest.java     | 17 ++++++++++++++++-
 1 file changed, 16 insertions(+), 1 deletion(-)

diff --git a/core-java-8/src/test/java/com/baeldung/collectors/Java8CollectorsUnitTest.java b/core-java-8/src/test/java/com/baeldung/collectors/Java8CollectorsUnitTest.java
index bad1c32e4a..9ace27e38f 100644
--- a/core-java-8/src/test/java/com/baeldung/collectors/Java8CollectorsUnitTest.java
+++ b/core-java-8/src/test/java/com/baeldung/collectors/Java8CollectorsUnitTest.java
@@ -39,6 +39,7 @@ import static org.assertj.core.api.Assertions.assertThatThrownBy;
 public class Java8CollectorsUnitTest {
 
     private final List<String> givenList = Arrays.asList("a", "bb", "ccc", "dd");
+    private final List<String> listWithDuplicates = Arrays.asList("a", "bb", "c", "d", "bb");
 
     @Test
     public void whenCollectingToList_shouldCollectToList() throws Exception {
@@ -48,12 +49,19 @@ public class Java8CollectorsUnitTest {
     }
 
     @Test
-    public void whenCollectingToList_shouldCollectToSet() throws Exception {
+    public void whenCollectingToSet_shouldCollectToSet() throws Exception {
         final Set<String> result = givenList.stream().collect(toSet());
 
         assertThat(result).containsAll(givenList);
     }
 
+    @Test
+    public void givenContainsDuplicateElements_whenCollectingToSet_shouldAddDuplicateElementsOnlyOnce() throws Exception {
+        final Set<String> result = listWithDuplicates.stream().collect(toSet());
+
+        assertThat(result).hasSize(4);
+    }
+
     @Test
     public void whenCollectingToCollection_shouldCollectToCollection() throws Exception {
         final List<String> result = givenList.stream().collect(toCollection(LinkedList::new));
@@ -83,6 +91,13 @@ public class Java8CollectorsUnitTest {
         assertThat(result).containsEntry("a", 1).containsEntry("bb", 2).containsEntry("ccc", 3).containsEntry("dd", 2);
     }
 
+    @Test
+    public void givenContainsDuplicateElements_whenCollectingToMap_shouldThrowException() throws Exception {
+        assertThatThrownBy(() -> {
+            listWithDuplicates.stream().collect(toMap(Function.identity(), String::length));
+        }).isInstanceOf(IllegalStateException.class);
+    }
+
     @Test
     public void whenCollectingAndThen_shouldCollect() throws Exception {
         final List<String> result = givenList.stream().collect(collectingAndThen(toList(), ImmutableList::copyOf));