[GitHub] [arrow] wesm commented on a change in pull request #7718: PARQUET-1882: Buffered Reads should allow for 0 length

[GitBox <gi...@apache.org>]

wesm commented on a change in pull request #7718:
URL: https://github.com/apache/arrow/pull/7718#discussion_r453335961



##########
File path: cpp/src/parquet/file_serialize_test.cc
##########
@@ -398,6 +400,48 @@ TEST(TestBufferedRowGroupWriter, MultiPageDisabledDictionary) {
   }
 }
 
+TEST(Roundtrip, AllNulls) {
+  auto primitiveNode =
+      PrimitiveNode::Make("nulls", Repetition::OPTIONAL, nullptr, Type::INT32);
+  schema::NodeVector columns({primitiveNode});
+
+  auto rootNode = GroupNode::Make("root", Repetition::REQUIRED, columns, nullptr);
+
+  auto sink = CreateOutputStream();
+
+  auto fileWriter =
+      ParquetFileWriter::Open(sink, std::static_pointer_cast<GroupNode>(rootNode));
+  auto rowGroupWriter = fileWriter->AppendRowGroup();
+  auto columnWriter = static_cast<Int32Writer*>(rowGroupWriter->NextColumn());
+
+  int32_t values[3];
+  int16_t defLevels[] = {0, 0, 0};
+
+  columnWriter->WriteBatch(3, defLevels, nullptr, values);
+
+  columnWriter->Close();
+  rowGroupWriter->Close();
+  fileWriter->Close();
+
+  ReaderProperties props = default_reader_properties();
+  props.enable_buffered_stream();
+  PARQUET_ASSIGN_OR_THROW(auto buffer, sink->Finish());
+
+  auto source = std::make_shared<::arrow::io::BufferReader>(buffer);
+  auto file_reader = ParquetFileReader::Open(source);
+
+  auto fileReader = ParquetFileReader::Open(source, props);
+  auto rowGroupReader = fileReader->RowGroup(0);
+  auto columnReader = std::static_pointer_cast<Int32Reader>(rowGroupReader->Column(0));
+
+  int64_t valuesRead;
+  defLevels[0] = -1;
+  defLevels[1] = -1;
+  defLevels[2] = -1;
+  columnReader->ReadBatch(3, defLevels, nullptr, values, &valuesRead);
+  EXPECT_THAT(defLevels, ElementsAre(0, 0, 0));

Review comment:
       Should de-camel-case this test




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