code: def test_plot_univariate():
      """Tests plot_univariate function"""
      time_col = "time"
      value_col = "val"
      df = pd.DataFrame(
          {
              time_col: [
                  dt(2018, 1, 1, 0, 0, 1),
                  dt(2018, 1, 1, 0, 0, 2),
                  dt(2018, 1, 1, 0, 0, 3),
              ],
              value_col: [1, 2, 3],
          }
      )
      fig = plot_univariate(df, time_col, value_col)
      assert fig.data[0].name == value_col
      assert fig.layout.xaxis.title.text == time_col
      assert fig.layout.yaxis.title.text == value_col
      assert fig.layout.title.text == f"{value_col} vs {time_col}"
      assert fig.data[0].x.shape[0] == df.shape[0]
      assert fig.data[0].line.color == "rgb(32, 149, 212)"
      assert fig.data[0].mode == "lines"
      assert fig.layout.showlegend
  
      fig = plot_univariate(
          df,
          time_col,
          value_col,
          xlabel="x-axis",
          ylabel="y-axis",
          title="new title",
          color="blue",
          showlegend=False,
      )
      assert fig.layout.xaxis.title.text == "x-axis"
      assert fig.layout.yaxis.title.text == "y-axis"
      assert fig.data[0].line.color == "blue"
      assert fig.layout.title.text == "new title"
      assert not fig.layout.showlegend
  
imports: import datetime
  from datetime import datetime
  from functools import partial
  import numpy
  import pandas
  import pytest
  from pandas.testing import assert_frame_equal
  from plotly.colors import DEFAULT_PLOTLY_COLORS
  from testfixtures import LogCapture
  import greykite.common.constants
  from greykite.common.evaluation import EvaluationMetricEnum
  from greykite.common.viz.timeseries_plotting import add_groupby_column
  from greykite.common.viz.timeseries_plotting import flexible_grouping_evaluation
  from greykite.common.viz.timeseries_plotting import grouping_evaluation
  from greykite.common.viz.timeseries_plotting import plot_dual_axis_figure
  from greykite.common.viz.timeseries_plotting import plot_forecast_vs_actual
  from greykite.common.viz.timeseries_plotting import plot_multivariate
  from greykite.common.viz.timeseries_plotting import plot_multivariate_grouped
  from greykite.common.viz.timeseries_plotting import plot_univariate
  from greykite.common.viz.timeseries_plotting import split_range_into_groups
label_desc: Use image node_id 3 for calling a global function with example usage: test_plot_univariate() without return types