code: def test_no_implementations():
      f = Dispatcher("f")
      assert raises(NotImplementedError, lambda: f("hello"))
  
imports: from sympy.multipledispatch.dispatcher import Dispatcher, MDNotImplementedError, MethodDispatcher, halt_ordering, restart_ordering, ambiguity_register_error_ignore_dup
  from sympy.testing.pytest import raises, warns
label_desc: Use image node_id 15 for calling a global function with example usage: test_no_implementations() without return types