code: def test_3_2_1():
      """
      Test that the arguments to 'then' are optional.
      """
  
      p1 = Promise()
      p2 = p1.then()
      p3 = Promise()
      p4 = p3.then()
      p1.do_resolve(5)
      p3.do_reject(Exception("How dare you!"))
  
imports: from promise import Promise
  from .utils import assert_exception
  from threading import Event
label_desc: Use image node_id 1 for calling a global function with example usage: test_3_2_1() without return types