Add test for coalescing null values with time window aggregation

Author: kosiew

test-coalesce-null.py

@@ -0,0 +1,43 @@
+from pyarrow import flight
+from datafusion import SessionContext
+
+ctx = SessionContext()
+
+test_data = [
+    {
+        "id": 1,
+        "created_at": "2024-09-07 10:01:05",
+        "content": "First entry in first minute",
+    },
+    {
+        "id": 2,
+        "created_at": "2024-09-07 10:01:45",
+        "content": "Second entry in first minute",
+    },
+    {
+        "id": 3,
+        "created_at": "2024-09-07 10:03:10",
+        "content": "First entry in third minute",
+    },
+    {
+        "id": 4,
+        "created_at": "2024-09-07 10:03:55",
+        "content": "Second entry in third minute",
+    },
+]
+
+ctx.from_pylist(test_data, "count_me")
+
+sql = """ SELECT
+DATE_BIN(INTERVAL '1 minute', created_at) AS time_window,
+        COUNT(*) AS count
+    FROM
+        count_me
+
+GROUP BY
+    time_window
+ORDER BY
+    time_window;"""
+
+df = ctx.sql(sql)
+df.to_arrow_table()