scikit-learn
diff --git a/‎sklearn/pipeline.py
Lines changed: 2 additions & 2 deletions b/‎sklearn/pipeline.py
Lines changed: 2 additions & 2 deletions
diff --git a/‎sklearn/tests/test_pipeline.py
Lines changed: 27 additions & 2 deletions b/‎sklearn/tests/test_pipeline.py
Lines changed: 27 additions & 2 deletions
@@ -1106,7 +1106,7 @@ def get_metadata_routing(self):
         router = MetadataRouter(owner=self.__class__.__name__)
 
         # first we add all steps except the last one
-        for _, name, trans in self._iter(with_final=False):
+        for _, name, trans in self._iter(with_final=False, filter_passthrough=True):
             method_mapping = MethodMapping()
             # fit, fit_predict, and fit_transform call fit_transform if it
             # exists, or else fit and transform
@@ -1140,7 +1140,7 @@ def get_metadata_routing(self):
             router.add(method_mapping=method_mapping, **{name: trans})
 
         final_name, final_est = self.steps[-1]
-        if not final_est:
+        if final_est is None or final_est == "passthrough":
             return router
 
         # then we add the last step
 
@@ -17,7 +17,11 @@
 from sklearn.datasets import load_iris
 from sklearn.decomposition import PCA, TruncatedSVD
 from sklearn.dummy import DummyRegressor
-from sklearn.ensemble import HistGradientBoostingClassifier
+from sklearn.ensemble import (
+    HistGradientBoostingClassifier,
+    RandomForestClassifier,
+    RandomTreesEmbedding,
+)
 from sklearn.exceptions import NotFittedError
 from sklearn.feature_extraction.text import CountVectorizer
 from sklearn.feature_selection import SelectKBest, f_classif
@@ -27,7 +31,7 @@
 from sklearn.model_selection import train_test_split
 from sklearn.neighbors import LocalOutlierFactor
 from sklearn.pipeline import FeatureUnion, Pipeline, make_pipeline, make_union
-from sklearn.preprocessing import StandardScaler
+from sklearn.preprocessing import FunctionTransformer, StandardScaler
 from sklearn.svm import SVC
 from sklearn.utils._metadata_requests import COMPOSITE_METHODS, METHODS
 from sklearn.utils._testing import (
@@ -1828,5 +1832,26 @@ def test_routing_passed_metadata_not_supported(method):
         getattr(pipe, method)([[1]], sample_weight=[1], prop="a")
 
 
+@pytest.mark.usefixtures("enable_slep006")
+def test_pipeline_with_estimator_with_len():
+    """Test that pipeline works with estimators that have a `__len__` method."""
+    pipe = Pipeline(
+        [("trs", RandomTreesEmbedding()), ("estimator", RandomForestClassifier())]
+    )
+    pipe.fit([[1]], [1])
+    pipe.predict([[1]])
+
+
+@pytest.mark.usefixtures("enable_slep006")
+@pytest.mark.parametrize("last_step", [None, "passthrough"])
+def test_pipeline_with_no_last_step(last_step):
+    """Test that the pipeline works when there is not last step.
+
+    It should just ignore and pass through the data on transform.
+    """
+    pipe = Pipeline([("trs", FunctionTransformer()), ("estimator", last_step)])
+    assert pipe.fit([[1]], [1]).transform([[1], [2], [3]]) == [[1], [2], [3]]
+
+
 # End of routing tests
 # ====================