Add tests for null scalar binaryops (#10828)

Add tests for binaryops between two null scalars as per #10791 (comment)

This is technically `1307` tests but they only take about 5 seconds to run.

Authors:
  - https://github.com/brandon-b-miller

Approvers:
  - GALI PREM SAGAR (https://github.com/galipremsagar)

URL: #10828

python/cudf/cudf/tests/test_binops.py

@@ -902,7 +902,7 @@ def dtype_scalar(val, dtype):
         return dtype.type(val)
 
 
-def make_valid_scalar_add_data():
+def make_scalar_add_data():
     valid = set()
 
     # to any int, we may add any kind of
@@ -968,7 +968,7 @@ def make_invalid_scalar_add_data():
     return sorted(list(invalid))
 
 
-@pytest.mark.parametrize("dtype_l,dtype_r", make_valid_scalar_add_data())
+@pytest.mark.parametrize("dtype_l,dtype_r", make_scalar_add_data())
 def test_scalar_add(dtype_l, dtype_r):
     test_value = 1
 
@@ -1481,6 +1481,41 @@ def test_scalar_power_invalid(dtype_l, dtype_r):
         lval_gpu**rval_gpu
 
 
+def make_scalar_null_binops_data():
+    return (
+        [(operator.add, *dtypes) for dtypes in make_scalar_add_data()]
+        + [(operator.sub, *dtypes) for dtypes in make_scalar_difference_data()]
+        + [(operator.mul, *dtypes) for dtypes in make_scalar_product_data()]
+        + [(operator.add, *dtypes) for dtypes in make_scalar_add_data()]
+        + [
+            (operator.floordiv, *dtypes)
+            for dtypes in make_scalar_floordiv_data()
+        ]
+        + [
+            (operator.truediv, *dtypes)
+            for dtypes in make_scalar_truediv_data()
+        ]
+        + [(operator.mod, *dtypes) for dtypes in make_scalar_remainder_data()]
+        + [(operator.pow, *dtypes) for dtypes in make_scalar_power_data()]
+    )
+
+
+@pytest.mark.parametrize("op,dtype_l,dtype_r", make_scalar_null_binops_data())
+def test_scalar_null_binops(op, dtype_l, dtype_r):
+    lhs = cudf.Scalar(cudf.NA, dtype=dtype_l)
+    rhs = cudf.Scalar(cudf.NA, dtype=dtype_r)
+
+    result = op(lhs, rhs)
+    assert result.value is cudf.NA
+
+    # make sure dtype is the same as had there been a valid scalar
+    valid_lhs = cudf.Scalar(0, dtype=dtype_l)
+    valid_rhs = cudf.Scalar(0, dtype=dtype_r)
+
+    valid_result = op(valid_lhs, valid_rhs)
+    assert result.dtype == valid_result.dtype
+
+
 @pytest.mark.parametrize(
     "date_col",
     [