Python 的单元测试 Unittest

Author: yifei / Created: May 31, 2018, 9:52 a.m. / Modified: May 31, 2018, 9:54 a.m. / Edit

General rules for writing unittest

Each test unit must be fully independent. Each of them must be able to run alone, and also within the test suite, regardless of the order they are called. The implication of this rule is that each test must be loaded with a fresh dataset and may have to do some cleanup afterwards. This is usually handled by setUp() and tearDown() methods.

Try hard to make tests that run fast. If one single test needs more than a few milliseconds to run, development will be slowed down or the tests will not be run as often as is desirable. In some cases, tests can’t be fast because they need a complex data structure to work on, and this data structure must be loaded every time the test runs. Keep these heavier tests in a separate test suite that is run by some scheduled task, and run all other tests as often as needed.

If you are in the middle of a development session and have to interrupt your work, it is a good idea to write a broken unit test about what you want to develop next. When coming back to work, you will have a pointer to where you were and get back on track faster.

Use long and descriptive names for testing functions. The style guide here is slightly different than that of running code, where short names are often preferred. The reason is testing functions are never called explicitly. square() or even sqr() is ok in running code, but in testing code you would have names such as test_square_of_number_2(),test_square_negative_number(). These function names are displayed when a test fails, and should be as descriptive as possible.

When something goes wrong or has to be changed, and if your code has a good set of tests, you or other maintainers will rely largely on the testing suite to fix the problem or modify a given behavior. Therefore the testing code will be read as much as or even more than the running code. A unit test whose purpose is unclear is not very helpful in this case.

Another use of the testing code is as an introduction to new developers. When someone will have to work on the code base, running and reading the related testing code is often the best they can do. They will or should discover the hot spots, where most difficulties arise, and the corner cases. If they have to add some functionality, the first step should be to add a test and, by this means, ensure the new functionality is not already a working path that has not been plugged into the interface.

basic unittest

import unittest

def fun(x):
    return x + 1

class MyTest(unittest.TestCase):
    def setUp(self):
        # bootstrapping
    def tearDown(self):
        #clean up
    def test(self):
        self.assertEqual(fun(3), 4)

Unittest 中的 assert 方法:

方法 含义
assertEqual(a, b) a == b
assertNotEqual(a, b) a != b
assertTrue(x) bool(x) is True
assertFalse(x) bool(x) is False
assertIs(a, b) a is b
assertIsNot(a, b) a is not b
assertIsNone(x) x is None
assertIsNotNone(x) x is not None
assertIn(a, b) a in b
assertNotIn(a, b) a not in b
assertIsInstance(a, b) isinstance(a, b)
assertNotIsInstance(a, b) not isinstance(a, b)

save it as and run it by:

python -m unittest fun_test

Note: only method starts with test is run by unittest module

unittest这个库没有按照PEP8来, 看着就不爽


需要用 unicode, 需要用u prefix

需要转义 \n


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