The Hacker's Guide To Python 单元测试

基本方式

python中提供了非常简单的单元测试方式，利用nose包中的nosetests命令可以实现简单的批量测试。

安装nose包

sudo pip install nose

编辑测试文件

# test_true.py
def test_true():
    assert True

def test_false():
    assert False

执行测试

# 命令， nosetests命令会加载所有以test_开头的文件，并执行所有以test_开头的函数
nosetests -v
# 输出
test_true.test_true ... ok
test_true.test_false ... FAIL

======================================================================
FAIL: test_true.test_false
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/usr/local/lib/python2.7/site-packages/nose/case.py", line 197, in runTest
    self.test(*self.arg)
  File "/xxxx/workspace/py/test/test_true.py", line 5, in test_false
    assert False
AssertionError

----------------------------------------------------------------------
Ran 2 tests in 0.007s

FAILED (failures=1

unittest是python提供了单元测试的标准库。

# 为了兼容python 2.6和2.7
try:
    import unittest2 as unittest
except ImportError:
    import unittest

class TestKey(unittest.TestCase):
    def test_keyh(self):
        a = ['a']
        b = ['a', 'b']
        self.assertEqual(a, b)

输出如下，

test_keyh (test_true.TestKey) ... FAIL

======================================================================
FAIL: test_keyh (test_true.TestKey)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/home/y/workspace/py/test/test_true.py", line 8, in test_keyh
    self.assertEqual(a, b)
AssertionError: Lists differ: ['a'] != ['a', 'b']

Second list contains 1 additional elements.
First extra element 1:
b

- ['a']
+ ['a', 'b']

----------------------------------------------------------------------
Ran 1 test in 0.006s

FAILED (failures=1)

此外，unittest.skipIf可以通过判断条件来选择是否进行测试，

class TestSkipped(unittest.TestCase):
    @unitttest.skip("Do not run this")
    def test_failt(self):
        self.fail("This should not be run")

    @unittest.skipIf(mylib is None, "mylib is not available")
    def test_mylib(self):
        self.assertEqual(1, 1)

此外，自定义setUp和tearDown函数可以单元测试开始和结束时自动调用。

fixtures

fixtures模块可以用来临时改变当前的测试环境。

import fixtures
import os

class TestEnviron(fixtures.TestWithFixtures):
    def test_environ(self):
        fixture = self.useFixture(
                fixtures.EnvironmentVariable("FOOBAR", "42")) # 临时增加一个环境变量FOOBAR
        self.assertEqual(os.environ.get("FOOBAR"), "42")

    def test_environ_no_fixture(self):
        self.assertEqual(os.environ.get("FOOBAR"), None) # 上面增加的环境变量的操作对于其他函数无效

mock

mock模块可以用来进行模拟测试，其主要功能就是模拟一个函数，类或实例的行为。

由于网络测试环境的特殊性，最常用的使用就是模拟网络请求，具体例子如下，

# test_mock.py
import requests
import unittest
import mock

class WhereIsPythonError(Exception):
    pass

def is_python():
    try:
        r = requests.get("http://python.org")
    except IOError:
        pass
    else:
        if r.status_code == 200:
            return 'is python' in r.content
    raise WhereIsPythonError('something happened')

def get_fake_get(status_code, content):
    m = mock.Mock()
    m.status_code = status_code
    m.content = content
    def fake_get(url):
        return m
    return fake_get

def raise_get(url):
    raise IOError("unable to fetch url %s" % url)

class TestPython(unittest.TestCase):
    @mock.patch('requests.get', get_fake_get(
        200, 'is python, hello'
        ))
    def test_python_is(self):
        self.assertTrue(is_python())

    @mock.patch('requests.get', get_fake_get(
        200, 'is not python, hello'
        ))
    def test_python_is_not(self):
        self.assertFalse(is_python())

输出如下，

# 命令
nosetests --tests=test_mock -v
# 结果
test_python_is (test_mock.TestPython) ... ok
test_python_is_not (test_mock.TestPython) ... ok

----------------------------------------------------------------------
Ran 2 tests in 0.001s

OK