code: def test_format_single_feature():
      assert format_single_feature("a") == "a"
      assert format_single_feature("<>") == "&lt;&gt;"
      assert format_single_feature("aa bb") == (
          "aa"
          "<span "
          'style="background-color: hsl(120, 80%, 70%); margin: 0 0.1em 0 0.1em" '
          'title="A space symbol">'
          "&emsp;"
          "</span>"
          "bb"
      )
      assert format_single_feature("  aa bb ", weight=-1) == (
          "<span "
          'style="background-color: hsl(0, 80%, 70%); margin: 0 0.1em 0 0" '
          'title="2 space symbols">'
          "&emsp;"
          "&emsp;"
          "</span>"
          "aa"
          "<span "
          'style="background-color: hsl(0, 80%, 70%); margin: 0 0.1em 0 0.1em" '
          'title="A space symbol">'
          "&emsp;"
          "</span>"
          "bb"
          "<span "
          'style="background-color: hsl(0, 80%, 70%); margin: 0 0 0 0.1em" '
          'title="A space symbol">'
          "&emsp;"
          "</span>"
      )
  
imports: import re
  import pytest
  import numpy
  from sklearn.datasets import make_regression
  from sklearn.linear_model import LinearRegression
  from eli5.base import DocWeightedSpans, FeatureWeight
  from eli5 import explain_weights_sklearn, explain_prediction_sklearn
  from eli5.formatters import format_as_text, format_as_html, format_html_styles, FormattedFeatureName
  from eli5.formatters.html import _format_unhashed_feature, render_weighted_spans, _format_single_feature, _format_feature, remaining_weight_color_hsl, weight_color_hsl
  from eli5.formatters.text_helpers import get_char_weights, PreparedWeightedSpans
  from .utils import write_html
label_desc: Use image node_id 8 for calling a global function with example usage: test_format_single_feature() without return types