code: def test_derived_units_must_exist_in_unit_system():
      for unit_system in UnitSystem._unit_systems.values():
          for preferred_unit in unit_system.derived_units.values():
              units = preferred_unit.atoms(Quantity)
              for unit in units:
                  assert (
                      unit in unit_system._units
                  ), f"Unit {unit} is not in unit system {unit_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 8 for calling a global function with example usage: test_derived_units_must_exist_in_unit_system() without return types