code: def test_body_masscenter_vel():
      A = Body("A")
      N = ReferenceFrame("N")
      B = Body("B", frame=N)
      A.masscenter.set_vel(N, N.z)
      assert A.masscenter_vel(B) == N.z
      assert A.masscenter_vel(N) == N.z
  
imports: from sympy import Symbol, symbols, sin, cos, Matrix, zeros, simplify
  from sympy.physics.vector import Point, ReferenceFrame, dynamicsymbols, Dyadic
  from sympy.physics.mechanics import inertia, Body
  from sympy.testing.pytest import raises
label_desc: Use image node_id 7 for calling a global function with example usage: test_body_masscenter_vel() without return types