updating Java9ObjectsAPIUnitTest (eugenp#2430)

* updating Java9ObjectsAPIUnitTest

* some more changes to test

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

@@ -10,17 +10,27 @@
 import static org.hamcrest.MatcherAssert.assertThat;
 
 public class Java9ObjectsAPIUnitTest {
-
+
+    private List<String> aMethodReturningNullList(){
+        return null;
+    }
+
     @Test
     public void givenNullObject_whenRequireNonNullElse_thenElse(){
-        assertThat(Objects.<List>requireNonNullElse(null, Collections.EMPTY_LIST),
-                is(Collections.EMPTY_LIST));
+        List<String> aList = Objects.<List>requireNonNullElse(
+                aMethodReturningNullList(), Collections.EMPTY_LIST);
+        assertThat(aList, is(Collections.EMPTY_LIST));
+    }
+
+    private List<String> aMethodReturningNonNullList(){
+        return List.of("item1", "item2");
     }
 
     @Test
     public void givenObject_whenRequireNonNullElse_thenObject(){
-        assertThat(Objects.<List>requireNonNullElse(List.of("item1", "item2"),
-                Collections.EMPTY_LIST), is(List.of("item1", "item2")));
+        List<String> aList = Objects.<List>requireNonNullElse(
+                aMethodReturningNonNullList(), Collections.EMPTY_LIST);
+        assertThat(aList, is(List.of("item1", "item2")));
     }
 
     @Test(expected = NullPointerException.class)
@@ -30,8 +40,8 @@ public void givenNull_whenRequireNonNullElse_thenException(){
 
     @Test
     public void givenObject_whenRequireNonNullElseGet_thenObject(){
-        assertThat(Objects.<List>requireNonNullElseGet(null, List::of),
-                is(List.of()));
+        List<String> aList = Objects.<List>requireNonNullElseGet(null, List::of);
+        assertThat(aList, is(List.of()));
     }
 
     @Test