test: Test the case where no handler for the x-sql-datatype is available

singer_sdk/connectors/sql.py

@@ -400,10 +400,16 @@ def _get_type_from_schema(self, schema: dict) -> sa.types.TypeEngine | None:
             SQL type if one can be determined, None otherwise.
         """
         # Check x-sql-datatype first
-        if x_sql_datatype := schema.get("x-sql-datatype"):  # noqa: SIM102
+        if x_sql_datatype := schema.get("x-sql-datatype"):
             if handler := self._sql_datatype_mapping.get(x_sql_datatype):
                 return self._invoke_handler(handler, schema)
 
+            warnings.warn(
+                f"This target does not support the x-sql-datatype '{x_sql_datatype}'",
+                UserWarning,
+                stacklevel=2,
+            )
+
         # Check if this is a string with format then
         if schema.get("type") == "string" and "format" in schema:  # noqa: SIM102
             if (format_type := self._handle_format(schema)) is not None:

tests/core/test_connector_sql.py

@@ -724,6 +724,15 @@ def test_annotation_sql_datatype(self):
         result = json_schema_to_sql.to_sql_type(jsonschema_type)
         assert isinstance(result, sa.types.JSON)
 
+        unknown_type = {"type": ["string"], "x-sql-datatype": "unknown"}
+        with pytest.warns(
+            UserWarning,
+            match="This target does not support the x-sql-datatype",
+        ):
+            result = json_schema_to_sql.to_sql_type(unknown_type)
+
+        assert isinstance(result, sa.types.VARCHAR)
+
 
 def test_bench_discovery(benchmark, tmp_path: Path):
     def _discover_catalog(connector):