test: Include None in partitions

- Already works, but I wanna add some optimizations for the single partition case
- `pc.unique` can be used directly on a lot of `ChunkedArray` types, but `filter` will drop nulls by default, so needs some care if present

Author: dangotbanned

tests/plan/frame_partition_by_test.py

@@ -16,7 +16,11 @@
 
 @pytest.fixture
 def data() -> Data:
-    return {"a": ["a", "b", "a", "b", "c"], "b": [1, 2, 1, 3, 3], "c": [5, 4, 3, 2, 1]}
+    return {
+        "a": ["a", "b", "a", None, "b", "c"],
+        "b": [1, 2, 1, 5, 3, 3],
+        "c": [5, 4, 3, 6, 2, 1],
+    }
 
 
 @pytest.mark.parametrize(
@@ -27,6 +31,7 @@ def data() -> Data:
             [
                 {"a": ["a", "a"], "b": [1, 1], "c": [5, 3]},
                 {"a": ["b", "b"], "b": [2, 3], "c": [4, 2]},
+                {"a": [None], "b": [5], "c": [6]},
                 {"a": ["c"], "b": [3], "c": [1]},
             ],
         ),
@@ -35,6 +40,7 @@ def data() -> Data:
             [
                 {"b": [1, 1], "c": [5, 3]},
                 {"b": [2, 3], "c": [4, 2]},
+                {"b": [5], "c": [6]},
                 {"b": [3], "c": [1]},
             ],
         ),
@@ -63,11 +69,12 @@ def test_partition_by_single(
             [
                 {"a": ["a", "a"], "b": [1, 1], "c": [5, 3]},
                 {"a": ["b"], "b": [2], "c": [4]},
+                {"a": [None], "b": [5], "c": [6]},
                 {"a": ["b"], "b": [3], "c": [2]},
                 {"a": ["c"], "b": [3], "c": [1]},
             ],
         ),
-        (False, [{"c": [5, 3]}, {"c": [4]}, {"c": [2]}, {"c": [1]}]),
+        (False, [{"c": [5, 3]}, {"c": [4]}, {"c": [6]}, {"c": [2]}, {"c": [1]}]),
     ],
     ids=["include_key", "exclude_key"],
 )