new_contents: 
  import unittest
  
  import gmaps
  
  class TestHeatmapOptionsMixin(unittest.TestCase):
  
      def test_gradient_default_none(self):
          l = gmaps.maps._HeatmapOptionsMixin()
          assert l.gradient is None
  
      def test_gradient_default_values(self):
          l = gmaps.maps._HeatmapOptionsMixin(gradient=["blue", "red"])
          assert l.gradient == ["blue", "red"]
  
      def test_gradient_set_none(self):
          l = gmaps.maps._HeatmapOptionsMixin(gradient=["blue", "red"])
          l.gradient = None
          assert l.gradient is None
  
  
subject: Test options mixin