[GitHub] [arrow] jorgecarleitao commented on a change in pull request #8009: ARROW-9790: [Rust][Parquet]: Increase test coverage in arrow_reader.rs

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

jorgecarleitao commented on a change in pull request #8009:
URL: https://github.com/apache/arrow/pull/8009#discussion_r473249646



##########
File path: rust/parquet/src/arrow/arrow_reader.rs
##########
@@ -348,30 +348,101 @@ mod tests {
         ";
 
         let converter = Utf8ArrayConverter {};
-        single_column_reader_test::<
+        run_single_column_reader_tests::<
             ByteArrayType,
             StringArray,
             Utf8ArrayConverter,
             RandUtf8Gen,
-        >(2, 100, 2, message_type, 15, 50, converter);
+        >(2, message_type, &converter);
     }
 
-    fn single_column_reader_test<T, A, C, G>(
+    /// Parameters for single_column_reader_test
+    #[derive(Debug)]
+    struct TestOptions {
+        /// Number of row group to write to parquet (row group size =
+        /// num_row_groups / num_rows)
         num_row_groups: usize,
+        /// Total number of rows
         num_rows: usize,
-        rand_max: i32,
-        message_type: &str,
+        /// Size of batches to read back
         record_batch_size: usize,
+        /// Total number of batches to attempt to read.
+        /// `record_batch_size` * `num_iterations` should be greater
+        /// than `num_rows` to ensure the data can be read back completely
         num_iterations: usize,
-        converter: C,
+    }
+
+    impl TestOptions {
+        fn new(
+            num_row_groups: usize,
+            num_rows: usize,
+            record_batch_size: usize,
+            num_iterations: usize,
+        ) -> Self {
+            TestOptions {
+                num_row_groups,
+                num_rows,
+                record_batch_size,
+                num_iterations,
+            }
+        }
+    }
+
+    /// Create a parquet file and then read it using
+    /// `ParquetFileArrowReader` using a standard set of parameters
+    /// `opts`.
+    ///
+    /// `rand_max` represents the maximum size of value to pass to to
+    /// value generator
+    fn run_single_column_reader_tests<T, A, C, G>(
+        rand_max: i32,
+        message_type: &str,
+        converter: &C,
     ) where
         T: DataType,
         G: RandGen<T>,
         A: PartialEq + Array + 'static,
         C: Converter<Vec<Option<T::T>>, A> + 'static,
     {
-        let values: Vec<Vec<T::T>> = (0..num_row_groups)
-            .map(|_| G::gen_vec(rand_max, num_rows))
+        let all_options = vec![
+            TestOptions::new(2, 100, 15, 50),
+            // batch size (5) so batches to fall on row group
+            // boundaries (25 rows in 3 row groups --> row groups of
+            // 10, 10, and 5) to test edge refilling edge cases.
+            TestOptions::new(3, 25, 5, 50),

Review comment:
       Since you felt the need to add a comment explaining the values, a tiny suggestion is to declare all members of `TestOptions` as `pub` and use 
   
   ```
   TestOptions {
       num_row_groups: 3,
       num_rows: 25,
       record_batch_size: 5,
       num_iterations: 50,
   }
   ```
   instead, to increase readability of the values' meaning.
   




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