chore: fix Multimodal Gemini modifies input DF (#1467)

* chore: add experimental blob url tests

* fix

* chore: fix Multimodal Gemini modifies input DF

* fix

Author: GarrettWu

bigframes/core/convert.py

@@ -54,7 +54,7 @@ def to_bf_series(
         bigframes.pandas.Series
     """
     if isinstance(obj, series.Series):
-        return obj
+        return obj.copy()
 
     if session is None:
         session = global_session.get_global_session()
@@ -118,7 +118,7 @@ def to_bf_dataframe(
     session: Optional[session.Session] = None,
 ) -> dataframe.DataFrame:
     if isinstance(obj, dataframe.DataFrame):
-        return obj
+        return obj.copy()
 
     if isinstance(obj, pd.DataFrame):
         if session is None:

tests/system/small/core/test_convert.py

@@ -56,4 +56,7 @@ def test_to_bf_dataframe(input, session):
 def test_to_bf_dataframe_with_bf_dataframe(session):
     bf = dataframe.DataFrame({"test": [1, 2, 3]}, session=session)
 
-    assert convert.to_bf_dataframe(bf, None, session) is bf
+    testing.assert_frame_equal(
+        convert.to_bf_dataframe(bf, None, session).to_pandas(),
+        bf.to_pandas(),
+    )

tests/unit/ml/test_golden_sql.py

@@ -66,6 +66,7 @@ def mock_y(mock_session):
     mock_y._session = mock_session
     mock_y.columns = pd.Index(["input_column_label"])
     mock_y.cache.return_value = mock_y
+    mock_y.copy.return_value = mock_y
 
     return mock_y
 
@@ -98,6 +99,7 @@ def mock_X(mock_y, mock_session):
     )
 
     mock_X.cache.return_value = mock_X
+    mock_X.copy.return_value = mock_X
 
     return mock_X