code: def testSlope(self):
      slope = self.__buildSlope([1, 2, 3, 2, 1], 3)
      self.assertEqual(slope[0], None)
      self.assertEqual(slope[1], None)
      self.assertEqual(round(slope[2], 2), 1.0)
      self.assertEqual(slope[3], 0.0)
      self.assertEqual(slope[4], -1.0)
  
file_path: pyalgotrade/testcases/technical_trend_test.py
imports: from .None import common
  from pyalgotrade.technical import linreg
  from pyalgotrade import dataseries
label_desc: Use image node_id 2 for calling the SlopeTest obj's underlying member method code with example usage: obj.testSlope() without return types