Add $setWindowFields sortBy validation corner case tests

docs/testing/TEST_COVERAGE.md

@@ -585,12 +585,12 @@ Same shape as §11, applied to a different axis: §11 covers expression operator
 - Frame validation errors (documents, range, time-range): invalid bound types, malformed arrays, conflicting modes — these are operator-agnostic
 - Stage-level parameter validation: verify the `$setWindowFields` stage document structure per the spec. For each parameter below, test both valid inputs (succeeds) and invalid inputs (errors with correct code):
   - `partitionBy`: optional. Valid: expression (`"$field"`), literal value, omitted (entire collection = one partition). Invalid: test is not needed — any expression is accepted.
-  - `sortBy`: optional in some cases, required in others. Valid: object with field-direction pairs (`{"field": 1}`, `{"a": 1, "b": -1}`), omitted when using unbounded `["unbounded", "unbounded"]` documents-mode window with a non-rank operator. Invalid/errors: omitted when using (1) rank/order operators (`$rank`, `$denseRank`, `$documentNumber`), (2) bounded documents-mode windows (e.g., `[-1, 1]`, `["unbounded", "current"]`, `["current", "unbounded"]`), (3) `$linearFill` operator, (4) range-mode or time-range-mode windows. Also invalid: non-object type, empty object, direction values other than 1/-1.
+  - `sortBy`: optional in some cases, required in others. Valid: object with field-direction pairs (`{"field": 1}`, `{"a": 1, "b": -1}`), omitted when using unbounded `["unbounded", "unbounded"]` documents-mode window with a non-rank operator. Invalid/errors: omitted when using (1) rank/order operators (`$rank`, `$denseRank`, `$documentNumber`), (2) bounded documents-mode windows (e.g., `[-1, 1]`, `["unbounded", "current"]`, `["current", "unbounded"]`), (3) `$linearFill` operator, (4) range-mode or time-range-mode windows. Also invalid: non-object type, empty object, direction values other than 1/-1. For range/time-range windows specifically: `null` (treated as omitted) and `{}` (no sort fields) are also rejected since range requires exactly one ascending sort field.
   - `output`: required. Valid: document with one or more output fields, each containing a window operator and optional `window` key; dotted field names create embedded documents (same semantics as `$addFields`/`$set`). Invalid: omitted, non-document type, empty document, output field with no recognized window operator.
   - `window`: optional per output field (omitting defaults to unbounded whole-partition). Valid: document with exactly one of `documents` or `range`. Invalid: empty document, both `documents` and `range` specified, unknown keys inside `window`, non-document type.
   - `window.documents`: valid: two-element array where each element is `"current"`, `"unbounded"`, or an integer; lower bound ≤ upper bound. Invalid: non-array, array with fewer or more than 2 elements, non-integer numeric bounds (e.g., 1.5), string values other than `"current"`/`"unbounded"`, lower bound > upper bound.
-  - `window.range`: valid: two-element array where each element is `"current"`, `"unbounded"`, or a number; lower bound ≤ upper bound; requires `sortBy` on a single field. Invalid: non-array, array with fewer or more than 2 elements, string values other than `"current"`/`"unbounded"`, lower bound > upper bound, `sortBy` with multiple fields.
-  - `window.unit`: optional; when specified, converts `range` window to time-based. Valid: `"year"`, `"quarter"`, `"month"`, `"week"`, `"day"`, `"hour"`, `"minute"`, `"second"`, `"millisecond"`. Invalid: unrecognized string, non-string type, used with `documents` mode (should be rejected or ignored — verify behavior).
+  - `window.range`: valid: two-element array where each element is `"current"`, `"unbounded"`, or a number; lower bound ≤ upper bound; requires `sortBy` on a single ascending field. Invalid: non-array, array with fewer or more than 2 elements, string values other than `"current"`/`"unbounded"`, lower bound > upper bound, `sortBy` with multiple fields, descending sort direction.
+  - `window.unit`: optional; when specified, converts `range` window to time-based. Valid: `"year"`, `"quarter"`, `"month"`, `"week"`, `"day"`, `"hour"`, `"minute"`, `"second"`, `"millisecond"`. Invalid: unrecognized string, non-string type, used with `documents` mode (should be rejected or ignored — verify behavior), fractional numeric bounds (e.g., 1.5 hours — time-range bounds must be integers).
   - Unknown top-level keys in the `$setWindowFields` stage document are rejected with an error.
 - Documents-mode frame boundaries: using `$sum` as a sample operator, verify that document-based frame boundary specifications (centered, trailing, leading, non-overlapping) correctly control which documents are selected into the window. Edge cases: empty frame, single-element frame, and frame wider than the partition.
 - Range-mode frame boundaries: using `$sum` as a sample operator, verify that numeric range-based frame bounds correctly define the window of documents selected for computation.

documentdb_tests/compatibility/tests/core/operator/stages/setWindowFields/test_setWindowFields_documents_frame_errors.py

@@ -573,3 +573,33 @@ def test_cumulative_documents_window_without_sortby(collection):
         },
     )
     assertFailureCode(result, 5339901, msg="cumulative documents window without sortBy rejected")
+
+
+# sortBy: null is treated as omitted — same error as missing sortBy
+
+
+def test_bounded_documents_window_with_null_sortby(collection):
+    """Bounded documents window [-1, 0] with sortBy: null produces error."""
+    collection.insert_many(SINGLE_DOC)
+    result = execute_command(
+        collection,
+        {
+            "aggregate": collection.name,
+            "pipeline": [
+                {
+                    "$setWindowFields": {
+                        "partitionBy": "$partition",
+                        "sortBy": None,
+                        "output": {
+                            "result": {
+                                "$sum": "$value",
+                                "window": {"documents": [-1, 0]},
+                            }
+                        },
+                    }
+                }
+            ],
+            "cursor": {},
+        },
+    )
+    assertFailureCode(result, 5339901, msg="bounded documents window with sortBy: null rejected")

documentdb_tests/compatibility/tests/core/operator/stages/setWindowFields/test_setWindowFields_range_frame_errors.py

@@ -281,6 +281,63 @@ def test_range_no_sortby(collection):
     assertFailureCode(result, 5339902, msg="range window without sortBy rejected")
 
 
+# sortBy: null and {} are treated as absent — same error as omitting sortBy entirely
+
+
+def test_range_null_sortby(collection):
+    """Range window with sortBy: null (treated as omitted) produces error 5339902."""
+    collection.insert_many(SINGLE_DOC)
+    result = execute_command(
+        collection,
+        {
+            "aggregate": collection.name,
+            "pipeline": [
+                {
+                    "$setWindowFields": {
+                        "partitionBy": "$partition",
+                        "sortBy": None,
+                        "output": {
+                            "result": {
+                                "$sum": "$value",
+                                "window": {"range": [-10, 10]},
+                            }
+                        },
+                    }
+                }
+            ],
+            "cursor": {},
+        },
+    )
+    assertFailureCode(result, 5339902, msg="range window with sortBy: null rejected")
+
+
+def test_range_empty_sortby(collection):
+    """Range window with sortBy: {} (empty object, no sort fields) produces error 5339902."""
+    collection.insert_many(SINGLE_DOC)
+    result = execute_command(
+        collection,
+        {
+            "aggregate": collection.name,
+            "pipeline": [
+                {
+                    "$setWindowFields": {
+                        "partitionBy": "$partition",
+                        "sortBy": {},
+                        "output": {
+                            "result": {
+                                "$sum": "$value",
+                                "window": {"range": [-10, 10]},
+                            }
+                        },
+                    }
+                }
+            ],
+            "cursor": {},
+        },
+    )
+    assertFailureCode(result, 5339902, msg="range window with sortBy: {} rejected")
+
+
 def test_range_descending_sort(collection):
     """Range mode with descending sort produces error 8947401."""
     collection.insert_many(SINGLE_DOC)

documentdb_tests/compatibility/tests/core/operator/stages/setWindowFields/test_setWindowFields_time_range_frame_errors.py

@@ -191,6 +191,65 @@ def test_time_range_unit_without_date_sortby(collection):
     assertFailureCode(result, 5429513, msg="time unit with non-date sortBy rejected")
 
 
+# Property [Fractional Bound with Unit]: time-range bounds must be integers
+
+
+def test_time_range_fractional_bound(collection):
+    """Range with fractional bound and time unit produces error."""
+    collection.insert_many(SINGLE_DATE_DOC)
+    result = execute_command(
+        collection,
+        {
+            "aggregate": collection.name,
+            "pipeline": [
+                {
+                    "$setWindowFields": {
+                        "partitionBy": "$partition",
+                        "sortBy": {"date": 1},
+                        "output": {
+                            "result": {
+                                "$sum": "$value",
+                                "window": {"range": [-1.5, 1.5], "unit": "hour"},
+                            }
+                        },
+                    }
+                }
+            ],
+            "cursor": {},
+        },
+    )
+    assertFailureCode(result, FAILED_TO_PARSE_ERROR, msg="fractional bound with time unit rejected")
+
+
+def test_time_range_fractional_lower_bound_only(collection):
+    """Range with fractional lower bound and integer upper bound with time unit produces error."""
+    collection.insert_many(SINGLE_DATE_DOC)
+    result = execute_command(
+        collection,
+        {
+            "aggregate": collection.name,
+            "pipeline": [
+                {
+                    "$setWindowFields": {
+                        "partitionBy": "$partition",
+                        "sortBy": {"date": 1},
+                        "output": {
+                            "result": {
+                                "$sum": "$value",
+                                "window": {"range": [-1.5, 2], "unit": "hour"},
+                            }
+                        },
+                    }
+                }
+            ],
+            "cursor": {},
+        },
+    )
+    assertFailureCode(
+        result, FAILED_TO_PARSE_ERROR, msg="fractional lower bound with time unit rejected"
+    )
+
+
 # Property [Bound Type Validation with Unit]: bounds must be numeric when unit is specified