add unit test

datafusion/src/physical_plan/expressions/nth_value.rs

@@ -164,3 +164,77 @@ impl WindowAccumulator for NthValueAccumulator {
         Ok(Some(self.value.clone()))
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::error::Result;
+    use crate::physical_plan::expressions::col;
+    use arrow::record_batch::RecordBatch;
+    use arrow::{array::*, datatypes::*};
+
+    fn test_i32_result(expr: Arc<NthValue>, expected: i32) -> Result<()> {
+        let arr: ArrayRef = Arc::new(Int32Array::from(vec![1, -2, 3, -4, 5, -6, 7, 8]));
+        let schema = Schema::new(vec![Field::new("arr", DataType::Int32, false)]);
+        let batch = RecordBatch::try_new(Arc::new(schema), vec![arr])?;
+
+        let mut acc = expr.create_accumulator()?;
+        let expr = expr.expressions();
+        let values = expr
+            .iter()
+            .map(|e| e.evaluate(&batch))
+            .map(|r| r.map(|v| v.into_array(batch.num_rows())))
+            .collect::<Result<Vec<_>>>()?;
+        let result = acc.scan_batch(batch.num_rows(), &values)?;
+        assert_eq!(false, result.is_some());
+        let result = acc.evaluate()?;
+        assert_eq!(Some(ScalarValue::Int32(Some(expected))), result);
+        Ok(())
+    }
+
+    #[test]
+    fn first_value() -> Result<()> {
+        let first_value = Arc::new(NthValue::first_value(
+            "first_value".to_owned(),
+            col("arr"),
+            DataType::Int32,
+        ));
+        test_i32_result(first_value, 1)?;
+        Ok(())
+    }
+
+    #[test]
+    fn last_value() -> Result<()> {
+        let last_value = Arc::new(NthValue::last_value(
+            "last_value".to_owned(),
+            col("arr"),
+            DataType::Int32,
+        ));
+        test_i32_result(last_value, 8)?;
+        Ok(())
+    }
+
+    #[test]
+    fn nth_value_1() -> Result<()> {
+        let nth_value = Arc::new(NthValue::nth_value(
+            "nth_value".to_owned(),
+            col("arr"),
+            DataType::Int32,
+            1,
+        )?);
+        test_i32_result(nth_value, 1)?;
+        Ok(())
+    }
+
+    #[test]
+    fn nth_value_2() -> Result<()> {
+        let nth_value = Arc::new(NthValue::nth_value(
+            "nth_value".to_owned(),
+            col("arr"),
+            DataType::Int32,
+            1,
+        )?);
+        test_i32_result(nth_value, -2)?;
+        Ok(())
+    }
+}