From 550debc0edf1ea3e8e80d9d54a545019b9e579b8 Mon Sep 17 00:00:00 2001
From: Lawrence Mitchell <lmitchell@nvidia.com>
Date: Wed, 12 Jun 2024 16:24:53 +0000
Subject: [PATCH] Add tests of implemented StringFunctions

Additionally, assert that we raise during translation for an unhandled function.
---
 python/cudf_polars/cudf_polars/dsl/expr.py    |  4 +-
 .../tests/expressions/test_stringfunction.py  | 41 +++++++++++++++++++
 2 files changed, 44 insertions(+), 1 deletion(-)
 create mode 100644 python/cudf_polars/tests/expressions/test_stringfunction.py

diff --git a/python/cudf_polars/cudf_polars/dsl/expr.py b/python/cudf_polars/cudf_polars/dsl/expr.py
index a81cdcbf0c3..bac58f73f80 100644
--- a/python/cudf_polars/cudf_polars/dsl/expr.py
+++ b/python/cudf_polars/cudf_polars/dsl/expr.py
@@ -689,7 +689,9 @@ def do_evaluate(
                 )
             )
         else:
-            raise NotImplementedError(f"StringFunction {self.name}")
+            raise NotImplementedError(
+                f"StringFunction {self.name}"
+            )  # pragma: no cover; handled by init raising
 
 
 class Sort(Expr):
diff --git a/python/cudf_polars/tests/expressions/test_stringfunction.py b/python/cudf_polars/tests/expressions/test_stringfunction.py
new file mode 100644
index 00000000000..198f35d376b
--- /dev/null
+++ b/python/cudf_polars/tests/expressions/test_stringfunction.py
@@ -0,0 +1,41 @@
+# SPDX-FileCopyrightText: Copyright (c) 2024 NVIDIA CORPORATION & AFFILIATES.
+# SPDX-License-Identifier: Apache-2.0
+from __future__ import annotations
+
+import pytest
+
+import polars as pl
+
+from cudf_polars import translate_ir
+from cudf_polars.testing.asserts import assert_gpu_result_equal
+
+
+def test_supported_stringfunction_expression():
+    ldf = pl.LazyFrame(
+        {
+            "a": ["a", "b", "cdefg", "h", "Wıth ünιcοde"],  # noqa: RUF001
+            "b": [0, 3, 1, -1, None],
+        }
+    )
+
+    query = ldf.select(
+        pl.col("a").str.starts_with("Z"),
+        pl.col("a").str.ends_with("h").alias("endswith_h"),
+        pl.col("a").str.to_lowercase().alias("lower"),
+        pl.col("a").str.to_uppercase().alias("upper"),
+    )
+    assert_gpu_result_equal(query)
+
+
+def test_unsupported_stringfunction():
+    ldf = pl.LazyFrame(
+        {
+            "a": ["a", "b", "cdefg", "h", "Wıth ünιcοde"],  # noqa: RUF001
+            "b": [0, 3, 1, -1, None],
+        }
+    )
+
+    q = ldf.select(pl.col("a").str.count_matches("e", literal=True))
+
+    with pytest.raises(NotImplementedError):
+        _ = translate_ir(q._ldf.visit())