Add tests covering magic methods of Expr objects (rapidsai#15996)

repr is not stable for now because the pylibcudf datatype repr is not stable (it includes the address).

Authors:
  - Lawrence Mitchell (https://github.com/wence-)

Approvers:
  - Bradley Dice (https://github.com/bdice)

URL: rapidsai#15996

python/cudf_polars/cudf_polars/dsl/expr.py

@@ -134,14 +134,14 @@ def is_equal(self, other: Any) -> bool:
         True if the two expressions are equal, false otherwise.
         """
         if type(self) is not type(other):
-            return False
+            return False  # pragma: no cover; __eq__ trips first
         return self._ctor_arguments(self.children) == other._ctor_arguments(
             other.children
         )
 
     def __eq__(self, other: Any) -> bool:
         """Equality of expressions."""
-        if type(self) != type(other) or hash(self) != hash(other):
+        if type(self) is not type(other) or hash(self) != hash(other):
             return False
         else:
             return self.is_equal(other)
@@ -196,7 +196,9 @@ def do_evaluate(
             are returned during translation to the IR, but for now we
             are not perfect.
         """
-        raise NotImplementedError(f"Evaluation of {type(self).__name__}")
+        raise NotImplementedError(
+            f"Evaluation of expression {type(self).__name__}"
+        )  # pragma: no cover; translation of unimplemented nodes trips first
 
     def evaluate(
         self,
@@ -266,7 +268,7 @@ def collect_agg(self, *, depth: int) -> AggInfo:
         """
         raise NotImplementedError(
             f"Collecting aggregation info for {type(self).__name__}"
-        )
+        )  # pragma: no cover; check_agg trips first
 
 
 class NamedExpr:
@@ -287,7 +289,7 @@ def __hash__(self) -> int:
 
     def __repr__(self) -> str:
         """Repr of the expression."""
-        return f"NamedExpr({self.name}, {self.value}"
+        return f"NamedExpr({self.name}, {self.value})"
 
     def __eq__(self, other: Any) -> bool:
         """Equality of two expressions."""

python/cudf_polars/tests/dsl/__init__.py

@@ -0,0 +1,6 @@
+# SPDX-FileCopyrightText: Copyright (c) 2024 NVIDIA CORPORATION & AFFILIATES.
+# SPDX-License-Identifier: Apache-2.0
+
+from __future__ import annotations
+
+__all__: list[str] = []

python/cudf_polars/tests/dsl/test_expr.py

@@ -0,0 +1,76 @@
+# SPDX-FileCopyrightText: Copyright (c) 2024 NVIDIA CORPORATION & AFFILIATES.
+# SPDX-License-Identifier: Apache-2.0
+
+from __future__ import annotations
+
+import pytest
+
+import cudf._lib.pylibcudf as plc
+
+from cudf_polars.dsl import expr
+
+
+def test_expression_equality_not_expression():
+    col = expr.Col(plc.DataType(plc.TypeId.INT8), "a")
+    assert not (col == "a")  # noqa: SIM201
+    assert col != "a"
+
+
+@pytest.mark.parametrize("dtype", [plc.TypeId.INT8, plc.TypeId.INT16])
+def test_column_ne_dtypes_differ(dtype):
+    a = expr.Col(plc.DataType(dtype), "a")
+    b = expr.Col(plc.DataType(plc.TypeId.FLOAT32), "a")
+    assert a != b
+
+
+@pytest.mark.parametrize("dtype", [plc.TypeId.INT8, plc.TypeId.INT16])
+def test_column_ne_names_differ(dtype):
+    a = expr.Col(plc.DataType(dtype), "a")
+    b = expr.Col(plc.DataType(dtype), "b")
+    assert a != b
+
+
+@pytest.mark.parametrize("dtype", [plc.TypeId.INT8, plc.TypeId.INT16])
+def test_column_eq_names_eq(dtype):
+    a = expr.Col(plc.DataType(dtype), "a")
+    b = expr.Col(plc.DataType(dtype), "a")
+    assert a == b
+
+
+def test_expr_hashable():
+    a = expr.Col(plc.DataType(plc.TypeId.INT8), "a")
+    b = expr.Col(plc.DataType(plc.TypeId.INT8), "b")
+    c = expr.Col(plc.DataType(plc.TypeId.FLOAT32), "c")
+
+    collection = {a, b, c}
+    assert len(collection) == 3
+    assert a in collection
+    assert b in collection
+    assert c in collection
+
+
+def test_namedexpr_hashable():
+    b = expr.NamedExpr("b", expr.Col(plc.DataType(plc.TypeId.INT8), "a"))
+    c = expr.NamedExpr("c", expr.Col(plc.DataType(plc.TypeId.INT8), "a"))
+
+    collection = {b, c}
+
+    assert len(collection) == 2
+
+    assert b in collection
+    assert c in collection
+
+
+def test_namedexpr_ne_values():
+    b1 = expr.NamedExpr("b1", expr.Col(plc.DataType(plc.TypeId.INT8), "a"))
+    b2 = expr.NamedExpr("b2", expr.Col(plc.DataType(plc.TypeId.INT16), "a"))
+
+    assert b1 != b2
+
+
+@pytest.mark.xfail(reason="pylibcudf datatype repr not stable")
+def test_namedexpr_repr_stable():
+    b1 = expr.NamedExpr("b1", expr.Col(plc.DataType(plc.TypeId.INT8), "a"))
+    b2 = expr.NamedExpr("b1", expr.Col(plc.DataType(plc.TypeId.INT8), "a"))
+
+    assert repr(b1) == repr(b2)