diff --git a/src/skore/project.py b/src/skore/project.py
index 2a6cd3cf9..f9a5f62f3 100644
--- a/src/skore/project.py
+++ b/src/skore/project.py
@@ -1,5 +1,6 @@
 """"""
 
+import base64
 import json
 from dataclasses import dataclass
 from typing import Any, List
@@ -14,8 +15,7 @@ class Item:
     raw_class_name: str | None = None
 
 
-
-def transform(o: Any) -> Item:
+def transform(o: Any) -> Item | None:
     """Transform an object into an item."""
     try:
         serialized = json.dumps(o)
@@ -44,11 +44,12 @@ def transform(o: Any) -> Item:
                 raw_class_name="sklearn.base.BaseEstimator",
                 serialized=json.dumps(
                     {
-                        "skops": skops.io.dumps(o).decode(),
+                        "skops": base64.b64encode(skops.io.dumps(o)).decode("ascii"),
                         "html": sklearn.utils.estimator_html_repr(o),
                     }
                 ),
             )
+        return None
 
 
 class Project:
diff --git a/tests/test_dataframe_item.py b/tests/test_dataframe_item.py
deleted file mode 100644
index 95269400f..000000000
--- a/tests/test_dataframe_item.py
+++ /dev/null
@@ -1,10 +0,0 @@
-import pandas as pd
-from skore.project import DataFrameItem
-
-
-def test_dataframe_item():
-    df = pd.DataFrame([[1, 2, 3], [4, 5, 6]])
-    item = DataFrameItem(df)
-
-    assert item.raw == df
-    assert item.transformed == None
diff --git a/tests/unit/test_project.py b/tests/unit/test_project.py
index a8fa77293..a8ebdbe70 100644
--- a/tests/unit/test_project.py
+++ b/tests/unit/test_project.py
@@ -1,8 +1,8 @@
 import json
-import pandas
+
 import numpy
+import pandas
 import sklearn.svm
-import skops.io
 from skore.project import Item, transform
 
 
@@ -37,7 +37,10 @@ def test_transform_numpy_ndarray():
     assert actual == expected
 
 
-def test_transform_sklearn_base_baseestimator():
+def test_transform_sklearn_base_baseestimator(monkeypatch):
+    monkeypatch.setattr("sklearn.utils.estimator_html_repr", lambda _: "")
+    monkeypatch.setattr("skops.io.dumps", lambda _: "")
+
     o = sklearn.svm.SVC()
     actual = transform(o)
     expected = Item(
@@ -45,8 +48,8 @@ def test_transform_sklearn_base_baseestimator():
         raw_class_name="numpy.ndarray",
         serialized=json.dumps(
             {
-                "skops": skops.io.dumps(o).decode(),
-                "html": sklearn.utils.estimator_html_repr(o),
+                "skops": "",
+                "html": "",
             }
         ),
     )