code: def test_definition():
      # want to test if the system can have several units of the same dimension
      dm = Quantity("dm")
      base = (m, s)
      # base_dim = (m.dimension, s.dimension)
      ms = UnitSystem(base, (c, dm), "MS", "MS system")
      ms.set_quantity_dimension(dm, length)
      ms.set_quantity_scale_factor(dm, Rational(1, 10))
  
      assert set(ms._base_units) == set(base)
      assert set(ms._units) == {m, s, c, dm}
      # assert ms._units == DimensionSystem._sort_dims(base + (velocity,))
      assert ms.name == "MS"
      assert ms.descr == "MS system"
  
file_path: sympy/sympy/physics/units/tests/test_unitsystem.py
imports: from sympy.physics.units import DimensionSystem, joule, second, ampere
  from sympy.core.numbers import Rational
  from sympy.core.singleton import S
  from sympy.physics.units.definitions import c, kg, m, s
  from sympy.physics.units.definitions.dimension_definitions import length, time
  from sympy.physics.units.quantities import Quantity
  from sympy.physics.units.unitsystem import UnitSystem
  from sympy.physics.units.util import convert_to
label_desc: Use image node_id 1 for calling a global function with example usage: test_definition() without return types