JAVA-1470 Move 10 articles to libraries-4 module

libraries-4/src/test/java/com/baeldung/distinct/DistinctWithJavaFunctionUnitTest.java

@@ -0,0 +1,38 @@
+package com.baeldung.distinct;
+
+import static org.junit.Assert.assertTrue;
+import static com.baeldung.distinct.DistinctWithJavaFunction.distinctByKey;
+
+import java.util.List;
+import java.util.stream.Collectors;
+
+import org.junit.Before;
+import org.junit.Test;
+
+public class DistinctWithJavaFunctionUnitTest {
+    List<Person> personList;
+
+    @Before
+    public void init() {
+        personList = PersonDataGenerator.getPersonListWithFakeValues();
+    }
+
+    @Test
+    public void whenFilterListByName_thenSizeShouldBe4() {
+        List<Person> personListFiltered = personList.stream().filter(distinctByKey(p -> p.getName())).collect(Collectors.toList());
+        assertTrue(personListFiltered.size() == 4);
+    }
+
+    @Test
+    public void whenFilterListByAge_thenSizeShouldBe2() {
+        List<Person> personListFiltered = personList.stream().filter(distinctByKey(p -> p.getAge())).collect(Collectors.toList());
+        assertTrue(personListFiltered.size() == 2);
+    }
+
+    @Test
+    public void whenFilterListWithDefaultDistinct_thenSizeShouldBe5() {
+        List<Person> personListFiltered = personList.stream().distinct().collect(Collectors.toList());
+        assertTrue(personListFiltered.size() == 5);
+    }
+
+}