code: def test_3D_pathway_extension_velocity(self):
      self.pB.set_pos(
          self.pA,
          self.q1 * self.N.x
          - self.q2 * self.N.y
          + 2 * self.q3 * self.N.z,
      )
      length = sqrt(self.q1**2 + self.q2**2 + 4 * self.q3**2)
      expected = (
          self.q1 * self.q1d / length
          + self.q2 * self.q2d / length
          + 4 * self.q3 * self.q3d / length
      )
      assert simplify(self.pathway.extension_velocity - expected) == 0
  
imports: import pytest
  from sympy import Rational, Symbol, cos, pi, sin, sqrt
  from sympy.physics.mechanics import Force, LinearPathway, ObstacleSetPathway, PathwayBase, Point, ReferenceFrame, WrappingCylinder, WrappingGeometryBase, WrappingPathway, WrappingSphere, dynamicsymbols
  from sympy.simplify.simplify import simplify
label_desc: Use image node_id 15 for calling the TestLinearPathway obj's underlying member method code with example usage: obj.test_3D_pathway_extension_velocity() without return types