BAEL-7885: Simple tests for addAll (#16504)

* BAEL-7885: Simple tests for addAll

* BAEL-7885: Stream test example

core-java-modules/core-java-collections-array-list-2/pom.xml

@@ -12,6 +12,14 @@
         <version>0.0.1-SNAPSHOT</version>
     </parent>
 
+    <dependencies>
+        <dependency>
+            <groupId>org.apache.commons</groupId>
+            <artifactId>commons-collections4</artifactId>
+            <version>${apache.commons.version}</version>
+        </dependency>
+    </dependencies>
+
     <build>
         <plugins>
             <plugin>
@@ -28,5 +36,6 @@
     <properties>
         <maven-compiler-plugin.source>17</maven-compiler-plugin.source>
         <maven-compiler-plugin.target>17</maven-compiler-plugin.target>
+        <apache.commons.version>4.4</apache.commons.version>
     </properties>
 </project>

core-java-modules/core-java-collections-array-list-2/src/test/java/com/baeldung/addallnulls/AddAllWithNullsUnitTest.java

@@ -0,0 +1,89 @@
+package com.baeldung.addallnulls;
+
+import static org.assertj.core.api.Assertions.assertThatExceptionOfType;
+import static org.assertj.core.api.Assertions.assertThatNoException;
+
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Objects;
+import java.util.Optional;
+import java.util.stream.Stream;
+import org.apache.commons.collections4.CollectionUtils;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.MethodSource;
+import org.junit.jupiter.params.provider.NullSource;
+
+class AddAllWithNullsUnitTest {
+
+    @ParameterizedTest
+    @NullSource
+    void givenNull_whenAddAll_thenAddThrowsNPE(List<String> list) {
+        ArrayList<String> strings = new ArrayList<>();
+        assertThatExceptionOfType(NullPointerException.class).isThrownBy(() -> strings.addAll(list));
+    }
+
+    @ParameterizedTest
+    @NullSource
+    void givenNull_whenAddAllWithCheck_thenNoNPE(List<String> list) {
+        ArrayList<String> strings = new ArrayList<>();
+        assertThatNoException().isThrownBy(() -> {
+            if (list != null) {
+                strings.addAll(list);
+            }
+        });
+    }
+
+    @ParameterizedTest
+    @NullSource
+    void givenNull_whenAddAllWithCollectionCheck_thenNoNPE(List<String> list) {
+        ArrayList<String> strings = new ArrayList<>();
+        assertThatNoException().isThrownBy(() -> {
+            strings.addAll(CollectionUtils.emptyIfNull(list));
+        });
+    }
+
+    @ParameterizedTest
+    @NullSource
+    void givenNull_whenAddAllWithExternalizedCheck_thenNoNPE(List<String> list) {
+        ArrayList<String> strings = new ArrayList<>();
+        assertThatNoException().isThrownBy(() -> {
+            addIfNonNull(list, strings);
+        });
+    }
+
+    private static void addIfNonNull(List<String> list, ArrayList<String> strings) {
+        if (list != null) {
+            strings.addAll(list);
+        }
+    }
+
+    @ParameterizedTest
+    @NullSource
+    void givenNull_whenAddAllWithOptional_thenNoNPE(List<String> list) {
+        ArrayList<String> strings = new ArrayList<>();
+        assertThatNoException().isThrownBy(() -> {
+            Optional.ofNullable(list).ifPresent(strings::addAll);
+        });
+    }
+
+    @ParameterizedTest
+    @MethodSource("listProvider")
+    void givenCollectionOfNullableLists_whenFilter_thenNoNPE(List<List<String>> listOfLists) {
+        ArrayList<String> strings = new ArrayList<>();
+        assertThatNoException().isThrownBy(() -> {
+            listOfLists.stream().filter(Objects::nonNull).forEach(strings::addAll);
+        });
+    }
+
+    static Stream<List<List<String>>> listProvider() {
+        ArrayList<List<String>> lists = new ArrayList<>();
+        lists.add(null);
+        lists.add(List.of("Hello"));
+        lists.add(null);
+        lists.add(List.of("World"));
+        lists.add(null);
+        return Stream.of(
+          lists
+        );
+    }
+}