用于检查实例类型的 Python 测试 [英] Python test to check instance type

问题描述

我想在 python 中使用 unittest 来检查一个方法是否返回正确类的对象.

I want to use unittest in python to check if a method returns object of the right class.

网络中的每个示例都显示了对返回的类型"的测试.

Every example in the web shows tests for 'type' returned.

例如，要检查 或 ，我们可以使用:

For example, to check for <type 'list'> or <type 'type'> , we could use:

self.assertIsInstance(result, list)
self.assertIsInstance(result[0], tuple) 

我正在寻找的是一个检查 <class'sqlalchemy.orm.query.Query'>

What I am looking for is an example to check for <class'sqlalchemy.orm.query.Query'>

希望得到任何帮助.谢谢.

Would appreciate any help. Thankyou.

推荐答案

您可以使用 assertIsInstance()，大概使用 isinstance() 这是测试类型的推荐函数.您还可以根据上下文将 assertIs() 或 assertTrue() 与 type() 结合使用:

You could use assertIsInstance(), presumably using isinstance() which is the recommended function for testing types. You could also assertIs() or assertTrue() combined with type() depending on the context:

#assert.py
import unittest

class TestType(unittest.TestCase):

  def setUp(self):
      self.number = 1

  def test_assert_true(self):
      self.assertTrue(type(self.number) is int)

  def test_assert_is_instance(self):
      self.assertIsInstance(self.number, int)

  def test_assert_is_with_type(self):
      self.assertIs(type(self.number), int)

  def test_assert_is(self):
      self.assertIs(self.number, int)

if __name__ == '__main__':
    unittest.main()


$ python assert.py 

test_assert_is (__main__.TestType) ... FAIL
test_assert_is_instance (__main__.TestType) ... ok
test_assert_is_with_type (__main__.TestType) ... ok
test_assert_true (__main__.TestType) ... ok

======================================================================
FAIL: test_assert_is (__main__.TestType)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "assert.py", line 19, in test_assert_is
    self.assertIs(self.number, int)
AssertionError: 1 is not <type 'int'>

----------------------------------------------------------------------
Ran 4 tests in 0.000s

FAILED (failures=1)

test_assert_is(self) 的断言错误可能会让人相信 1 的类型不是整数，但它正在比较 1 表示的对象和描述整数类型的对象.这很可能是首选 isinstance() 的原因，因为它更详细地说明要检查的内容并且涉及的输入更少，因此通常更不容易出错.

The assertion error of the test_assert_is(self) might lead one to believe the type of 1 is not integer however it's comparing the object represented by 1 and the object that describes the type of an integer. This is most likely why isinstance() is preferred since it's more verbose about what it's checking and less typing is involved, so in general less error prone.

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