fix(pyspark): raise proper error when trying to generate sql

Author: cpcloud

ibis/backends/pyspark/__init__.py

@@ -704,3 +704,6 @@ def _register_failure(self):
             f"Cannot infer appropriate read function for input, "
             f"please call one of {msg} directly"
         )
+
+    def _to_sql(self, expr: ir.Expr, **kwargs) -> str:
+        raise NotImplementedError(f"Backend '{self.name}' backend doesn't support SQL")

ibis/backends/tests/test_generic.py

@@ -948,7 +948,9 @@ def test_memtable_construct(backend, con, monkeypatch):
     raises=NotImplementedError,
     reason="not a SQL backend",
 )
-@pytest.mark.notimpl(["pyspark"], raises=com.OperationNotDefinedError)
+@pytest.mark.notimpl(
+    ["pyspark"], reason="pyspark doesn't generate SQL", raises=NotImplementedError
+)
 @pytest.mark.notimpl(["druid"], reason="no sqlglot dialect", raises=ValueError)
 def test_many_subqueries(con, snapshot):
     def query(t, group_cols):