pytest - 使用pytest过程中的5大超级技巧（超长篇）

1、assert的各种使用场景

包含了几十种断言失败的各种场景，涉及断言的，可以查看pytest文档的 5.1.1（以 PDF 格式下载最新版本），举例几个常用的断言：

@pytest.mark.parametrize("param1, param2", [(3, 6)])
def test_generative(param1, param2):
    assert param1 * 2 < param2
    assert (3 * 2) < 6
    
def test_simple(self):
	def f():
		return 42
	def g():
		return 43
	assert f() == g()
	assert 42 == 43
	
def test_eq_long_text(self):
	a = "1" * 100 + "a" + "2" * 100
	b = "1" * 100 + "b" + "2" * 100
	assert a == b

2、基本模式和示例

2.1 更改命令行选项的默认值

# content of pytest.ini
[pytest]
addopts = -ra -q 

2.2 构建一个依赖于命令行选项的测试

根据命令行选项将不同的值传递给测试函数，运行用例：pytest -q test_sample.py --cmdopt=type3

# content of conftest.py
import pytest

def type_checker(value):
    msg = "cmdopt must specify a numeric type as typeNNN"
    if not value.startswith("type"):
        raise pytest.UsageError(msg)
    try:
        int(value[4:])
    except ValueError:
        raise pytest.UsageError(msg)
    return value


def pytest_addoption(parser):
    parser.addoption(
        "--cmdopt",
        action="store",
        default="type1",
        help="my option: type1 or type2",
        choices=("type1", "type2"),
        type=type_checker,
    )


@pytest.fixture
def cmdopt(request):
    return request.config.getoption("--cmdopt")

# content of test_sample.py

def test_answer(cmdopt):
    if cmdopt == "type1":
        print("first")
    elif cmdopt == "type2":
        print("second")
    assert 0

2.3 动态地添加命令行选项

# setuptools plugin
import sys
def pytest_load_initial_conftests(args):
	if "xdist" in sys.modules: # pytest-xdist plugin
		import multiprocessing
		
		num = max(multiprocessing.cpu_count() / 2, 1)
		args[:] = ["-n", str(num)] + args

2.4 控制跳过测试根据命令行选项

# content of conftest.py
import pytest
def pytest_addoption(parser):
	parser.addoption("--runslow", action="store_true", default=False, help="run slow tests" )
def pytest_configure(config):
	config.addinivalue_line("markers", "slow: mark test as slow to run")
def pytest_collection_modifyitems(config, items):
	if config.getoption("--runslow"):
		# --runslow given in cli: do not skip slow tests
		return
	skip_slow = pytest.mark.skip(reason="need --runslow option to run")
	for item in items:
		if "slow" in item.keywords:
			item.add_marker(skip_slow)

# content of test_module.py
import pytest
def test_func_fast():
	pass
@pytest.mark.slow
def test_func_slow():
	pass

2.5 编写良好的断言程序

# content of test_checkconfig.py
import pytest
def checkconfig(x):
	__tracebackhide__ = True
	if not hasattr(x, "config"):
		pytest.fail("not configured: {}".format(x))
def test_something():
	checkconfig(42)

2.6 检测是否从 pytest 运行中运行

# content of your_module.py
_called_from_test = False

# content of conftest.py
def pytest_configure(config):
	your_module._called_from_test = True

2.7 向测试报告题头添加信息

# content of conftest.py
def pytest_report_header(config):
	return "project deps: mylib-1.1"

2.8 分析测试持续时间

pytest --durations=3 test_some_are_slow.py

# content of test_some_are_slow.py
import time
def test_funcfast():
	time.sleep(0.1)
def test_funcslow1():
	time.sleep(0.2)
def test_funcslow2():
	time.sleep(0.3)

2.11 处理过程后的测试报告/失败

# content of conftest.py
import pytest
import os.path
@pytest.hookimpl(tryfirst=True, hookwrapper=True)
def pytest_runtest_makereport(item, call):
	# execute all other hooks to obtain the report object
	outcome = yield
	rep = outcome.get_result()
	# we only look at actual failing test calls, not setup/teardown
	if rep.when == "call" and rep.failed:
		mode = "a" if os.path.exists("failures") else "w"
		with open("failures", mode) as f:
			# let's also access a fixture for the fun of it
			if "tmp_path" in item.fixturenames:
				extra = " ({})".format(item.funcargs["tmp_path"])
			else:
				extra = "" f.write(rep.nodeid + extra + "\n")

# content of test_module.py
def test_fail1(tmp_path):
	assert 0
def test_fail2():
	assert 0

2.12 在固定设备中提供测试结果信息

# content of conftest.py
import pytest
@pytest.hookimpl(tryfirst=True, hookwrapper=True)
def pytest_runtest_makereport(item, call):
	# execute all other hooks to obtain the report object
	outcome = yield
	rep = outcome.get_result()
	# set a report attribute for each phase of a call, which can
	# be "setup", "call", "teardown"
	setattr(item, "rep_" + rep.when, rep)
@pytest.fixture
def something(request):
	yield
	# request.node is an "item" because we use the default
	# "function" scope
	if request.node.rep_setup.failed:
		print("setting up a test failed!", request.node.nodeid)
	elif request.node.rep_setup.passed:
		if request.node.rep_call.failed:
			print(