add Java unit tests for making list of list (#8111)

This PR is trying to add java binding support for making List of List based on #8046. But the existing jni API makeList has already supported to create List of List, this PR just add unit tests for making list of list.

Authors:
  - Bobby Wang (https://github.com/wbo4958)

Approvers:
  - Jason Lowe (https://github.com/jlowe)

URL: #8111

java/src/test/java/ai/rapids/cudf/ColumnVectorTest.java

@@ -4342,37 +4342,64 @@ void testMakeStruct() {
 
   @Test
   void testMakeListEmpty() {
-    final int numRows = 10;
-    try (ColumnVector expected =
+    final int numRows = 4;
+    List<List<String>> emptyListOfList = new ArrayList<>();
+    emptyListOfList.add(Arrays.asList());
+    try (
+        ColumnVector expectedList =
              ColumnVector.fromLists(
                  new ListType(false, new BasicType(false, DType.STRING)),
                  Arrays.asList(),
                  Arrays.asList(),
                  Arrays.asList(),
-                 Arrays.asList(),
-                 Arrays.asList(),
-                 Arrays.asList(),
-                 Arrays.asList(),
-                 Arrays.asList(),
-                 Arrays.asList(),
                  Arrays.asList());
-         ColumnVector created = ColumnVector.makeList(numRows, DType.STRING)) {
-      assertColumnsAreEqual(expected, created);
+         ColumnVector expectedListOfList = ColumnVector.fromLists(new HostColumnVector.ListType(false,
+                 new HostColumnVector.ListType(false,
+                     new HostColumnVector.BasicType(false, DType.STRING))),
+             emptyListOfList, emptyListOfList, emptyListOfList, emptyListOfList);
+
+         ColumnVector createdList = ColumnVector.makeList(numRows, DType.STRING);
+         ColumnVector createdListOfList = ColumnVector.makeList(createdList)) {
+      assertColumnsAreEqual(expectedList, createdList);
+      assertColumnsAreEqual(expectedListOfList, createdListOfList);
     }
   }
 
   @Test
   void testMakeList() {
-    try (ColumnVector expected =
-             ColumnVector.fromLists(
-                 new ListType(false, new BasicType(false, DType.INT32)),
-                 Arrays.asList(1, 3, 5),
-                 Arrays.asList(2, 4, 6));
+    List<Integer> list1 = Arrays.asList(1, 3);
+    List<Integer> list2 = Arrays.asList(2, 4);
+    List<Integer> list3 = Arrays.asList(5, 7, 9);
+    List<Integer> list4 = Arrays.asList(6, 8, 10);
+    List<List<Integer>> mainList1 = new ArrayList<>(Arrays.asList(list1, list3));
+    List<List<Integer>> mainList2 = new ArrayList<>(Arrays.asList(list2, list4));
+    try (ColumnVector expectedList1 =
+             ColumnVector.fromLists(new ListType(false,
+                 new BasicType(false, DType.INT32)), list1, list2);
+         ColumnVector expectedList2 =
+             ColumnVector.fromLists(new ListType(false,
+                 new BasicType(false, DType.INT32)), list3, list4);
+         ColumnVector expectedListOfList = ColumnVector.fromLists(new HostColumnVector.ListType(true,
+                 new HostColumnVector.ListType(true, new HostColumnVector.BasicType(true, DType.INT32))),
+             mainList1, mainList2);
          ColumnVector child1 = ColumnVector.fromInts(1, 2);
          ColumnVector child2 = ColumnVector.fromInts(3, 4);
          ColumnVector child3 = ColumnVector.fromInts(5, 6);
-         ColumnVector created = ColumnVector.makeList(child1, child2, child3)) {
-      assertColumnsAreEqual(expected, created);
+         ColumnVector child4 = ColumnVector.fromInts(7, 8);
+         ColumnVector child5 = ColumnVector.fromInts(9, 10);
+         ColumnVector createdList1 = ColumnVector.makeList(child1, child2);
+         ColumnVector createdList2 = ColumnVector.makeList(child3, child4, child5);
+         ColumnVector createdListOfList = ColumnVector.makeList(createdList1, createdList2);
+         HostColumnVector hcv = createdListOfList.copyToHost()) {
+
+      assertColumnsAreEqual(expectedList1, createdList1);
+      assertColumnsAreEqual(expectedList2, createdList2);
+      assertColumnsAreEqual(expectedListOfList, createdListOfList);
+
+      List<List<Integer>> ret1 = hcv.getList(0);
+      List<List<Integer>> ret2 = hcv.getList(1);
+      assertEquals(mainList1, ret1, "Lists don't match");
+      assertEquals(mainList2, ret2, "Lists don't match");
     }
   }