Fix offset value for generating test data in `parquet_chunked_reade…

…r_test.cu` (#15200)

In `parquet_chunked_reader_test.cu`, when generating test data, there is an `offset` value that should increase at every iteration. It is for shifting the null positions of each column such that the generating table will not have all nulls in the same rows. Somehow, it was left unchanged across all iterations, thus we need to fix that.

Authors:
  - Nghia Truong (https://github.com/ttnghia)
  - Karthikeyan (https://github.com/karthikeyann)

Approvers:
  - https://github.com/nvdbaranec
  - Bradley Dice (https://github.com/bdice)
  - Karthikeyan (https://github.com/karthikeyann)

URL: #15200

cpp/tests/io/parquet_chunked_reader_test.cu

@@ -66,8 +66,6 @@ auto write_file(std::vector<std::unique_ptr<cudf::column>>& input_columns,
                 std::size_t max_page_size_bytes = cudf::io::default_max_page_size_bytes,
                 std::size_t max_page_size_rows  = cudf::io::default_max_page_size_rows)
 {
-  // Just shift nulls of the next column by one position to avoid having all nulls in the same
-  // table rows.
   if (nullable) {
     // Generate deterministic bitmask instead of random bitmask for easy computation of data size.
     auto const valid_iter = cudf::detail::make_counting_transform_iterator(
@@ -83,6 +81,10 @@ auto write_file(std::vector<std::unique_ptr<cudf::column>>& input_columns,
         std::move(col),
         cudf::get_default_stream(),
         rmm::mr::get_current_device_resource());
+
+      // Shift nulls of the next column by one position, to avoid having all nulls
+      // in the same table rows.
+      ++offset;
     }
   }
 
@@ -988,7 +990,7 @@ TEST_F(ParquetChunkedReaderTest, TestChunkedReadWithListsOfStructs)
 
   {
     auto const [result, num_chunks] = chunked_read(filepath_with_nulls, 1'500'000);
-    EXPECT_EQ(num_chunks, 4);
+    EXPECT_EQ(num_chunks, 5);
     CUDF_TEST_EXPECT_TABLES_EQUAL(*expected_with_nulls, *result);
   }