为模拟assert_used_once_with()指定“类Foo的任何实例”？

Question

在 中assert_called_once_with，如何指定参数是“Foo 类的任何实例”？

例如：

class Foo(): pass
def f(x): pass
def g(): f(Foo())
import __main__
from unittest import mock

mock.ANY当然通过：

with mock.patch.object(__main__, 'f') as mock_f:
  g()
  mock_f.assert_called_once_with(mock.ANY)

当然，Foo 的另一个实例不会通过。

with mock.patch.object(__main__, 'f') as mock_f:
  g()
  mock_f.assert_called_once_with(Foo())

AssertionError: Expected call: f(<__main__.Foo object at 0x7fd38411d0b8>)
                  Actual call: f(<__main__.Foo object at 0x7fd384111f98>)

我可以将什么作为我的预期参数，以便 Foo 的任何实例都将使断言通过？

Answer 1

一个简单的解决方案是分两步完成此操作：

with mock.patch.object(__main__, 'f') as mock_f:
    g()
    mock_f.assert_called_once()
    self.assertIsInstance(mock_f.mock_calls[0].args[0], Foo)

但是，如果你看看以下的实现ANY：

class _ANY(object):
    "A helper object that compares equal to everything."

    def __eq__(self, other):
        return True

    def __ne__(self, other):
        return False

    def __repr__(self):
        return '<ANY>'

ANY = _ANY()

你可以看到它只是一个等于任何东西的对象。因此，您可以定义自己的等效项，它等于 的任何实例Foo：

class AnyFoo:
    "A helper object that compares equal to every instance of Foo."

    def __eq__(self, other):
        return isinstance(other, Foo)

    def __ne__(self, other):
        return not isinstance(other, Foo)

    def __repr__(self):
        return '<ANY Foo>'


ANY_FOO = AnyFoo()

或者更一般地说：

class AnyInstanceOf:
    "A helper object that compares equal to every instance of the specified class."

    def __init__(self, cls):
        self.cls = cls

    def __eq__(self, other):
        return isinstance(other, self.cls)

    def __ne__(self, other):
        return not isinstance(other, self.cls)

    def __repr__(self):
        return f"<ANY {self.cls.__name__}>"


ANY_FOO = AnyInstanceOf(Foo)

无论哪种方式，您都可以像您想的那样使用它ANY：

with mock.patch.object(__main__, 'f') as mock_f:
    g()
    mock_f.assert_called_once_with(ANY_FOO)