Python Testing with pytest

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技术

Author

Brian Okken

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Date

Jun 3, 2023 → Jun 18, 2023

Summary

偏应用的书籍，本身没有太多思考，但是比官方文档写的好很多了

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CH1: Getting Started with pytest

• pytest: With no arguments, pytest searches the local directory and subdirectories for tests.

• pytest <filename>: Runs the tests in one file

• pytest <filename> <filename> ...: Runs the tests in multiple named files

• pytest<dirname>: Starts in a particular directory (or more than one) and recursively searches for tests

• The -v or --verbose command-line flag is used to reveal more verbose output.

• The --tb=no command-line flag is used to to turn off tracebacks. 通常用在运行一个文件夹下所有测试代码的时候，看起来简洁一些

• Test files should be named test_<something>.py or <something>_test.py.

• Test methods and functions should be named test_<something>.

• Test classes should be named Test<Something>.

• PASSED (.)—The test ran successfully.

• FAILED (F)—The test did not run successfully.

• SKIPPED (s)—The test was skipped. You can tell pytest to skip a test by using either the @pytest.mark.skip() or @pytest.mark.skipif() decorators

• XFAIL (x)—The test was not supposed to pass, and it ran and failed. You can tell pytest that a test is expected to fail by using the @pytest.mark.xfail()decorator

• XPASS (X)—The test was marked with xfail, but it ran and passed.

• ERROR (E)—An exception happened either during the execution of a fixture or hook function, and not during the execution of a test function.

CH2:Writing Test Functions

def test_with_fail():
	c1 = Card("sit there", "brian")
	c2 = Card("do something", "okken")
	if c1 != c2:
		pytest.fail("they don't match")

from cards import Card
import pytest

def assert_identical(c1: Card, c2: Card):
    __tracebackhide__ = True
    assert c1 == c2
    if c1.id != c2.id:
        pytest.fail(f"id's don't match. {c1.id} != {c2.id}")


def test_identical():
    c1 = Card("foo", id=123)
    c2 = Card("foo", id=123)
    assert_identical(c1, c2)


def test_identical_fail():
    c1 = Card("foo", id=123)
    c2 = Card("foo", id=456)
    assert_identical(c1, c2)

def test_no_path_raises():
	with pytest.raises(TypeError):
		cards.CardsDB()

# 用正则表达式来匹配返回的异常
def test_raises_with_info():
    match_regex = "missing 1 .* positional argument"
    with pytest.raises(TypeError, match=match_regex):
        cards.CardsDB()

# 用 assert来匹配返回的异常
def test_raises_with_info_alt():
    with pytest.raises(TypeError) as exc_info:
        cards.CardsDB()
    expected = "missing 1 required positional argument"
    assert expected in str(exc_info.value)

• 通过 将类似的一组测试函数封装为class来作为一个组，这样在用的时候可以 pytest path/test_module.py::TestClass 来测试该class内的测试方法

• 通过 pytest -k pattern 来测试名称匹配的测试函数

• 使用 -vv 参数可以进一步增加 pytest 的输出详细程度

• 推荐 "Given-When-Then" 或者 "Arrange-Act-Assert" 这种测试代码结构的方式：
1. Given（Arrange）：测试数据和环境的准备阶段，也就是测试的前置条件。
2. When（Act）：测试代码执行的阶段，也就是测试的操作和行为。
3. Then（Assert）：测试结果的验证阶段，也就是测试的后置条件。

CH3: pytest Fixtures

from pathlib import Path
from tempfile import TemporaryDirectory
import cards

import pytest

@pytest.fixture()
def cards_db():
    with TemporaryDirectory() as db_dir:
        db_path = Path(db_dir)
        db = cards.CardsDB(db_path)
        yield db
        db.close()

def test_empty(cards_db):
    assert cards_db.count() == 0

========================== test session starts ==========================
collected 2 items
test_mod_scope.py
		SETUP M cards_db
				ch3/test_mod_scope.py::test_empty (fixtures used: cards_db).
				ch3/test_mod_scope.py::test_two (fixtures used: cards_db).
		TEARDOWN M cards_db
=========================== 2 passed in 0.03s ===========================

• scope='function'。Run once per test function. The setup portion is run before each test using the fixture. The teardown portion is run after each test using the fixture.This is the default scope used when no scope parameter is specified.

• scope='class'。Run once per test class, regardless of how many test methods are in the class.

• scope='module'。Run once per module, regardless of how many test functions or methods or other fixtures in the module use it.

• scope='package'。Run once per package, or test directory, regardless of how many test functions or methods or other fixtures in the package use it.

• scope='session'。Run once per session. All test methods and functions using a fixture of session scope share one setup and teardown call.

@pytest.fixture(scope="session")
def db():
	"""CardsDB object connected to a temporary database"""
	with TemporaryDirectory() as db_dir:
	db_path = Path(db_dir)
	db_ = cards.CardsDB(db_path)
		yield db_
	db_.close()


@pytest.fixture(scope="function")
def cards_db(db):
	"""CardsDB object that's empty"""
	db.delete_all()
	return db

CH4:Builtin Fixtures

• tmp_path，会得到一个临时路径，scope=function

• tmp_path_factory，通过调用mktemp()得到一个临时路径，scope=secession

• 以上两者创建的路径均为pathlib.Path对象

def test_tmp_path(tmp_path):
	file = tmp_path / "file.txt"
	file.write_text("Hello")
	assert file.read_text() == "Hello"

def test_tmp_path_factory(tmp_path_factory):
	path = tmp_path_factory.mktemp("sub")
	file = path / "file.txt"
	file.write_text("Hello")
	assert file.read_text() == "Hello"

• capsys，测试命令行应用

import cards

def test_version_v2(capsys):
	cards.cli.version() # 先调用这个查看版本
	output = capsys.readouterr().out.rstrip() # 然后捕捉输出
	assert output == cards.__version__

def test_disabled(capsys):
	with capsys.disabled():
		print("\ncapsys disabled print")

• monkeypatch，用于临时修改对象、字典、环境变量、Python搜索路径或当前目录。不管测试是否通过，之后都会复原
• setattr(target, name, value, raising=True)—Sets an attribute
• delattr(target, name, raising=True)—Deletes an attribute
• setitem(dic, name, value)—Sets a dictionary entry
• delitem(dic, name, raising=True)—Deletes a dictionary entry
• setenv(name, value, prepend=None)—Sets an environment variable
• delenv(name, raising=True)—Deletes an environment variable
• syspath_prepend(path)—Prepends path to sys.path, which is Python’s list of import locations
• chdir(path)—Changes the current working directory

CH5: Parametrization

• Parametrizing Functions，@pytest.mark.parametrize()

• Parametrizing Fixtures，@pytest.fixture(params=())

• Parametrizing with pytest_generate_tests， pytest_generate_tests 比较复杂，先跳过

import pytest
from cards import Card

# Parametrizing Functions

@pytest.mark.parametrize(
	"start_summary, start_state",
	[
		("write a book", "done"),
		("second edition", "in prog"),
		("create a course", "todo"),
	],
	)
def test_finish(cards_db, start_summary, start_state):
	initial_card = Card(summary=start_summary, state=start_state)
	index = cards_db.add_card(initial_card)
	cards_db.finish(index)
	card = cards_db.get_card(index)
	assert card.state == "done"

# Parametrizing Fixtures

@pytest.fixture(params=["done", "in prog", "todo"])
def start_state(request):
	return request.param

def test_finish(cards_db, start_state):
	c = Card("write a book", state=start_state)
	index = cards_db.add_card(c)
	cards_db.finish(index)
	card = cards_db.get_card(index)
	assert card.state == "done"