add polars series unit tests

Author: tswast

bigframes/testing/polars_session.py

@@ -95,10 +95,17 @@ def __init__(self):
 
     def read_pandas(self, pandas_dataframe, write_engine="default"):
         # override read_pandas to always keep data local-only
-        if isinstance(pandas_dataframe, pandas.Series):
+        if isinstance(pandas_dataframe, (pandas.Series, pandas.Index)):
             pandas_dataframe = pandas_dataframe.to_frame()
         local_block = bigframes.core.blocks.Block.from_local(pandas_dataframe, self)
-        return bigframes.dataframe.DataFrame(local_block)
+        bf_df = bigframes.dataframe.DataFrame(local_block)
+        if isinstance(pandas_dataframe, pandas.Series):
+            series = bf_df[bf_df.columns[0]]
+            series.name = pandas_dataframe.name
+            return series
+        if isinstance(pandas_dataframe, pandas.Index):
+            return bf_df.index
+        return bf_df
 
     @property
     def bqclient(self):