Add unit test for ToArrayOp with scalar subquery expression

Author: shuoweil

packages/bigframes/tests/unit/core/compile/sqlglot/expressions/snapshots/test_array_ops/test_to_array_with_subquery_expression/out.sql

@@ -0,0 +1,12 @@
+SELECT
+  [
+    COALESCE(
+      (
+        SELECT
+          COALESCE(SUM(bf_arr_reduce_uid), 0)
+        FROM UNNEST(`float_list_col`) AS bf_arr_reduce_uid
+      ),
+      0.0
+    )
+  ] AS `arr_subquery_coalesce`
+FROM `bigframes-dev`.`sqlglot_test`.`repeated_types` AS `bft_0`

packages/bigframes/tests/unit/core/compile/sqlglot/expressions/test_array_ops.py

@@ -104,3 +104,14 @@ def test_to_array_op(scalar_types_df: bpd.DataFrame, snapshot):
 
     sql = utils._apply_ops_to_sql(bf_df, list(ops_map.values()), list(ops_map.keys()))
     snapshot.assert_match(sql, "out.sql")
+
+
+def test_to_array_with_subquery_expression(repeated_types_df: bpd.DataFrame, snapshot):
+    reduced = ops.ArrayReduceOp(agg_ops.SumOp()).as_expr("float_list_col")
+    coalesced_reduced = ops.coalesce_op.as_expr(reduced, expression.const(0.0))
+    array_expr = ops.ToArrayOp().as_expr(coalesced_reduced)
+
+    sql = utils._apply_ops_to_sql(
+        repeated_types_df, [array_expr], ["arr_subquery_coalesce"]
+    )
+    snapshot.assert_match(sql, "out.sql")