text: # -*- coding: utf-8 -*-
  
  from sympy.physics.unitsystems.prefixes import PREFIXES, prefix_unit
  
  
  def test_prefix_operations():
      m = PREFIXES['m']
      k = PREFIXES['k']
      M = PREFIXES['M']
  
      assert m * k == 1
      assert k * k == M
      assert 1 / m == k
      assert k / m == M
  
  
  def test_prefix_unit():
      from sympy.physics.unitsystems import Unit, Dimension
  
      length = Dimension(length=1)
      m = Unit(length, abbrev="m")
  
      pref = {"m": PREFIXES["m"], "c": PREFIXES["c"], "d": PREFIXES["d"]}
  
      res = [Unit(length, abbrev="m", prefix=PREFIXES["m"]),
             Unit(length, abbrev="m", prefix=PREFIXES["c"]),
             Unit(length, abbrev="m", prefix=PREFIXES["d"])]
  
      assert set(prefix_unit(m, pref)) == set(res)
  