code for Java 9 Objects API (#2408)

core-java-9/src/test/java/com/baeldung/java9/language/Java9ObjectsAPIUnitTest.java

@@ -0,0 +1,72 @@
+package com.baeldung.java9.language;
+
+import org.junit.Test;
+
+import java.util.Collections;
+import java.util.List;
+import java.util.Objects;
+
+import static org.hamcrest.Matchers.*;
+import static org.hamcrest.MatcherAssert.assertThat;
+
+public class Java9ObjectsAPIUnitTest {
+
+    @Test
+    public void givenNullObject_whenRequireNonNullElse_thenElse(){
+        assertThat(Objects.<List>requireNonNullElse(null, Collections.EMPTY_LIST),
+                is(Collections.EMPTY_LIST));
+    }
+
+    @Test
+    public void givenObject_whenRequireNonNullElse_thenObject(){
+        assertThat(Objects.<List>requireNonNullElse(List.of("item1", "item2"),
+                Collections.EMPTY_LIST), is(List.of("item1", "item2")));
+    }
+
+    @Test
+    public void givenObject_whenRequireNonNullElseGet_thenObject(){
+        assertThat(Objects.<List>requireNonNullElseGet(null, List::of),
+                is(List.of()));
+    }
+
+    @Test
+    public void givenNumber_whenInvokeCheckIndex_thenNumber(){
+        int length = 5;
+
+        assertThat(Objects.checkIndex(4, length), is(4));
+
+        try{
+            Objects.checkIndex(5, length);
+        }catch(Exception ex){
+            assertThat(ex, instanceOf(IndexOutOfBoundsException.class));
+        }
+    }
+
+    @Test
+    public void givenSubRange_whenCheckFromToIndex_thenNumber(){
+        int length = 6;
+
+        assertThat(Objects.checkFromToIndex(2,length,length), is(2));
+
+        try{
+            Objects.checkFromToIndex(2,7,length);
+        }catch(Exception ex){
+            assertThat(ex, instanceOf(IndexOutOfBoundsException.class));
+        }
+    }
+
+    @Test
+    public void giveSubRange_whenCheckFromIndexSize_thenNumber(){
+        int length = 6;
+
+        assertThat(Objects.checkFromToIndex(2,5,length), is(2));
+
+        try{
+            Objects.checkFromToIndex(2,6,length);
+        }catch(Exception ex){
+            assertThat(ex, instanceOf(IndexOutOfBoundsException.class));
+        }
+    }
+
+
+}