old_contents: import plotly.express as px
  import numpy as np
  import pandas as pd
  import pytest
  
  
  @pytest.mark.skipif(
      not hasattr(pd.options.plotting, "backend"),
      reason="Currently installed pandas doesn't support plotting backends.",
  )
  @pytest.mark.parametrize(
      "pandas_fn,px_fn",
      [
          (lambda df: df.plot(), px.line),
          (lambda df: df.plot.scatter("A", "B"), lambda df: px.scatter(df, "A", "B"),),
          (lambda df: df.plot.line(), px.line),
          (lambda df: df.plot.area(), px.area),
          (lambda df: df.plot.bar(), px.bar),
          (lambda df: df.plot.barh(), lambda df: px.bar(df, orientation="h")),
          (lambda df: df.plot.box(), px.box),
          (lambda df: df.plot.hist(), px.histogram),
          (lambda df: df.boxplot(), px.box),
          (lambda df: df.hist(), px.histogram),
          (lambda df: df["A"].hist(), lambda df: px.histogram(df["A"])),
      ],
  )
  def test_pandas_equiv(pandas_fn, px_fn):
      pd.options.plotting.backend = "plotly"
      df = pd.DataFrame(np.random.randn(100, 4), columns=list("ABCD")).cumsum()
      assert pandas_fn(df) == px_fn(df)
  
new_contents: import plotly.express as px
  import numpy as np
  import pandas as pd
  import pytest
  
  
  @pytest.mark.skipif(
      not hasattr(pd.options.plotting, "backend"),
      reason="Currently installed pandas doesn't support plotting backends.",
  )
  @pytest.mark.parametrize(
      "pandas_fn,px_fn",
      [
          (lambda df: df.plot(), px.line),
          (lambda df: df.plot.scatter("A", "B"), lambda df: px.scatter(df, "A", "B"),),
          (lambda df: df.plot.line(), px.line),
          (lambda df: df.plot.area(), px.area),
          (lambda df: df.plot.bar(), px.bar),
          (lambda df: df.plot.barh(), lambda df: px.bar(df, orientation="h")),
          (lambda df: df.plot.box(), px.box),
          (lambda df: df.plot.hist(), px.histogram),
          (lambda df: df.boxplot(), px.box),
          (lambda df: df.hist(), px.histogram),
          (lambda df: df["A"].hist(), lambda df: px.histogram(df["A"])),
      ],
  )
  def test_pandas_equiv(pandas_fn, px_fn):
      pd.options.plotting.backend = "plotly"
      df = pd.DataFrame(np.random.randn(100, 4), columns=list("ABCD")).cumsum()
      assert pandas_fn(df) == px_fn(df)
  
  
  def test_pandas_example():
      pd.options.plotting.backend = "plotly"
      ts = pd.Series(np.random.randn(1000), index=pd.date_range("1/1/2000", periods=1000))
      df = pd.DataFrame(np.random.randn(1000, 4), index=ts.index, columns=list("ABCD"))
      fig = df.iloc[5].plot.bar()
      assert len(fig.data) == 1
  
subject: add test