stocks date to string and test_trendline_on_timeseries fix

Author: FBruzzesi

packages/python/plotly/plotly/data/__init__.py

@@ -252,9 +252,10 @@ def stocks(indexed=False, datetimes=False, return_type="pandas"):
 
     df = nw.from_native(
         _get_dataset("stocks", return_type=return_type), eager_only=True
-    )
+    ).with_columns(nw.col("date").cast(nw.String()))
+
     if datetimes:
-        df = df.with_columns(nw.col("date").cast(nw.Datetime(time_unit="ns")))
+        df = df.with_columns(nw.col("date").str.to_datetime())
 
     if indexed:  # then it must be pandas
         df = df.to_native().set_index("date")

packages/python/plotly/plotly/tests/test_optional/test_px/test_trendline.py

@@ -189,8 +189,9 @@ def test_ols_trendline_slopes():
         ("ewm", dict(alpha=0.5)),
     ],
 )
-def test_trendline_on_timeseries(constructor, mode, options):
-    df = nw.from_native(constructor(px.data.stocks().to_dict(orient="list")))
+def test_trendline_on_timeseries(backend, mode, options):
+
+    df = nw.from_native(px.data.stocks(return_type=backend))
 
     pd_err_msg = r"Could not convert value of 'x' \('date'\) into a numeric type."
     pl_err_msg = "conversion from `str` to `f64` failed in column 'date'"