text: import pytest
  from pybind11_tests import callbacks as m
  from threading import Thread
  
  
  def test_callbacks():
      from functools import partial
  
      def func1():
          return "func1"
  
      def func2(a, b, c, d):
          return "func2", a, b, c, d
  
      def func3(a):
          return "func3({})".format(a)
  
      assert m.test_callback1(func1) == "func1"
      assert m.test_callback2(func2) == ("func2", "Hello", "x", True, 5)
      assert m.test_callback1(partial(func2, 1, 2, 3, 4)) == ("func2", 1, 2, 3, 4)
      assert m.test_callback1(partial(func3, "partial")) == "func3(partial)"
      assert m.test_callback3(lambda i: i + 1) == "func(43) = 44"
  
      f = m.test_callback4()
      assert f(43) == 44
      f = m.test_callback5()
      assert f(number=43) == 44
  
  
  def test_bound_method_callback():
      # Bound Python method:
      class MyClass:
          def double(self, val):
              return 2 * val
  
      z = MyClass()
      assert m.test_callback3(z.double) == "func(43) = 86"
  
      z = m.CppBoundMethodTest()
      assert m.test_callback3(z.triple) == "func(43) = 129"
  
  
  def test_keyword_args_and_generalized_unpacking():
  
      def f(*args, **kwargs):
          return args, kwargs
  
      assert m.test_tuple_unpacking(f) == (("positional", 1, 2, 3, 4, 5, 6), {})
      assert m.test_dict_unpacking(f) == (("positional", 1), {"key": "value", "a": 1, "b": 2})
      assert m.test_keyword_args(f) == ((), {"x": 10, "y": 20})
      assert m.test_unpacking_and_keywords1(f) == ((1, 2), {"c": 3, "d": 4})
      assert m.test_unpacking_and_keywords2(f) == (
          ("positional", 1, 2, 3, 4, 5),
          {"key": "value", "a": 1, "b": 2, "c": 3, "d": 4, "e": 5}
      )
  
      with pytest.raises(TypeError) as excinfo:
          m.test_unpacking_error1(f)
      assert "Got multiple values for keyword argument" in str(excinfo.value)
  
      with pytest.raises(TypeError) as excinfo:
          m.test_unpacking_error2(f)
      assert "Got multiple values for keyword argument" in str(excinfo.value)
  
      with pytest.raises(RuntimeError) as excinfo:
          m.test_arg_conversion_error1(f)
      assert "Unable to convert call argument" in str(excinfo.value)
  
      with pytest.raises(RuntimeError) as excinfo:
          m.test_arg_conversion_error2(f)
      assert "Unable to convert call argument" in str(excinfo.value)
  
  
  def test_lambda_closure_cleanup():
      m.test_cleanup()
      cstats = m.payload_cstats()
      assert cstats.alive() == 0
      assert cstats.copy_constructions == 1
      assert cstats.move_constructions >= 1
  
  
  def test_cpp_function_roundtrip():
      """Test if passing a function pointer from C++ -> Python -> C++ yields the original pointer"""
  
      assert m.test_dummy_function(m.dummy_function) == "matches dummy_function: eval(1) = 2"
      assert (m.test_dummy_function(m.roundtrip(m.dummy_function)) ==
              "matches dummy_function: eval(1) = 2")
      assert m.roundtrip(None, expect_none=True) is None
      assert (m.test_dummy_function(lambda x: x + 2) ==
              "can't convert to function pointer: eval(1) = 3")
  
      with pytest.raises(TypeError) as excinfo:
          m.test_dummy_function(m.dummy_function2)
      assert "incompatible function arguments" in str(excinfo.value)
  
      with pytest.raises(TypeError) as excinfo:
          m.test_dummy_function(lambda x, y: x + y)
      assert any(s in str(excinfo.value) for s in ("missing 1 required positional argument",
                                                   "takes exactly 2 arguments"))
  
  
  def test_function_signatures(doc):
      assert doc(m.test_callback3) == "test_callback3(arg0: Callable[[int], int]) -> str"
      assert doc(m.test_callback4) == "test_callback4() -> Callable[[int], int]"
  
  
  def test_movable_object():
      assert m.callback_with_movable(lambda _: None) is True
  
  
  def test_async_callbacks():
      # serves as state for async callback
      class Item:
          def __init__(self, value):
              self.value = value
  
      res = []
  
      # generate stateful lambda that will store result in `res`
      def gen_f():
          s = Item(3)
          return lambda j: res.append(s.value + j)
  
      # do some work async
      work = [1, 2, 3, 4]
      m.test_async_callback(gen_f(), work)
      # wait until work is done
      from time import sleep
      sleep(0.5)
      assert sum(res) == sum([x + 3 for x in work])
  
  
  def test_async_async_callbacks():
      t = Thread(target=test_async_callbacks)
      t.start()
      t.join()
  