add test for reading small batches

rust/datafusion/src/datasource/parquet.rs

@@ -406,6 +406,25 @@ mod tests {
  };
  use std::env;
 
+ #[test]
+ fn read_small_batches() {
+ let table = load_table("alltypes_plain.parquet");
+
+ let projection = None;
+ let scan = table.scan(&projection, 2).unwrap();
+ let mut it = scan[0].lock().unwrap();
+
+ let mut count = 0;
+ while let Some(batch) = it.next().unwrap() {
+ assert_eq!(11, batch.num_columns());
+ assert_eq!(2, batch.num_rows());
+ count += 1;
+ }
+
+ // we should have seen 4 batches of 2 rows
+ assert_eq!(4, count);
+ }
+
  #[test]
  fn read_alltypes_plain_parquet() {
  let table = load_table("alltypes_plain.parquet");