Error nicely when transforming if not fitted

ibisml/core.py

@@ -379,6 +379,11 @@ def _fit_table(
     def _transform_table(
         self, table: ir.Table, targets: tuple[str, ...] = (), index: str | None = None
     ) -> ir.Table:
+        if not self.is_fitted():
+            raise ValueError(
+                "This Recipe instance is not fitted yet. Call `fit` with appropriate "
+                "arguments before using this recipe."
+            )
         if targets:
             table = table.drop(*targets)
 

tests/test_core.py

@@ -338,3 +338,10 @@ def test_normalize_table_polars_errors():
     X = pl.DataFrame({"x": [1, 2]})
     with pytest.raises(TypeError, match="must also be a polars"):
         normalize_table(X, object())
+
+
+@pytest.mark.parametrize("method", ["transform", "to_ibis", "to_pandas", "to_numpy"])
+def test_errors_nicely_if_not_fitted(table, method):
+    r = ml.Recipe(ml.Drop(~ml.numeric()), ml.ScaleStandard(ml.numeric()))
+    with pytest.raises(ValueError, match="not fitted"):
+        getattr(r, method)(table)