move https://www.baeldung.com/java-hashmap-inside-list code to core-java-collections-list-4 module (#12671)

core-java-modules/core-java-collections-list-3/README.md

@@ -12,5 +12,4 @@ This module contains articles about the Java List collection
 - [How to Count Duplicate Elements in Arraylist](https://www.baeldung.com/java-count-duplicate-elements-arraylist)
 - [Finding the Differences Between Two Lists in Java](https://www.baeldung.com/java-lists-difference)
 - [List vs. ArrayList in Java](https://www.baeldung.com/java-list-vs-arraylist)
-- [How to Store HashMap<String, ArrayList> Inside a List](https://www.baeldung.com/java-hashmap-inside-list)
 - [[<-- Prev]](/core-java-modules/core-java-collections-list-2)

core-java-modules/core-java-collections-list-4/README.md

@@ -9,4 +9,5 @@ This module contains articles about the Java List collection
 - [Arrays.asList() vs Collections.singletonList()](https://www.baeldung.com/java-aslist-vs-singletonlist)
 - [Replace Element at a Specific Index in a Java ArrayList](https://www.baeldung.com/java-arraylist-replace-at-index)
 - [Difference Between Arrays.asList() and List.of()](https://www.baeldung.com/java-arrays-aslist-vs-list-of)
+- [How to Store HashMap<String, ArrayList> Inside a List](https://www.baeldung.com/java-hashmap-inside-list)
 - [[<-- Prev]](/core-java-modules/core-java-collections-list-3)

core-java-modules/core-java-collections-list-4/src/test/java/com/baeldung/list/listofhashmaps/ListOfHashMapsUnitTest.java

@@ -0,0 +1,37 @@
+package com.baeldung.list.listofhashmaps;
+
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.HashMap;
+import java.util.List;
+
+import org.junit.jupiter.api.Test;
+
+class ListOfHashMapsUnitTest {
+
+    @Test
+    void givenMaps_whenAddToList_thenListContainsMaps() {
+        List<HashMap<String, List<String>>> booksAuthorsMapsList = new ArrayList<>();
+        HashMap<String, List<String>> javaBooksAuthorsMap = new HashMap<>();
+        HashMap<String, List<String>> phpBooksAuthorsMap = new HashMap<>();
+
+        javaBooksAuthorsMap.put("Head First Java", Arrays.asList("Kathy Sierra", "Bert Bates"));
+        javaBooksAuthorsMap.put("Effective Java", Arrays.asList("Joshua Bloch"));
+        javaBooksAuthorsMap.put("OCA Java SE 8", Arrays.asList("Kathy Sierra", "Bert Bates", "Elisabeth Robson"));
+        phpBooksAuthorsMap.put("The Joy of PHP", Arrays.asList("Alan Forbes"));
+        phpBooksAuthorsMap.put("Head First PHP & MySQL", Arrays.asList("Lynn Beighley", "Michael Morrison"));
+
+        booksAuthorsMapsList.add(javaBooksAuthorsMap);
+        booksAuthorsMapsList.add(phpBooksAuthorsMap);
+
+        assertTrue(booksAuthorsMapsList.get(0)
+            .keySet()
+            .containsAll(new ArrayList<>(javaBooksAuthorsMap.keySet())));
+
+        assertTrue(booksAuthorsMapsList.get(1)
+            .keySet()
+            .containsAll(new ArrayList<>(phpBooksAuthorsMap.keySet())));
+    }
+}