python - Pytest:需要缓慢初始化的参数化测试

Question

我想用非常慢的 init 方法对一个类的随机参数进行测试。测试本身非常快，但需要一个耗时的初始化步骤。当然。我做这样的事情:

@pytest.mark.parametrize("params", LIST_OF_RANDOMIZED_PARAMS)
def test_one(params):
    state = very_slow_initialization(params)
    assert state.fast_test()

@pytest.mark.parametrize("params", LIST_OF_RANDOMIZED_PARAMS)
def test_two(params):
    state = very_slow_initialization(params)
    assert state.another_fast_test()

从我迄今为止不成功的尝试中我了解到:

1. 不支持使用参数化的 set_class(params) 方法初始化测试类
2. 使用初始化类的 fixture 每次仍然调用缓慢的初始化
3. 我可以预先创建一个包含所有初始化状态的列表，但是它们需要大量内存。此外，有时我喜欢在一夜之间运行大量随机测试，然后在第二天早上停止它们。这我需要准确地知道我应该进行多少次测试，以便所有初始化在此之前完成。
4. 如果可能的话，我更喜欢这样一种解决方案，即针对第一个参数运行两个测试，然后使用第二个参数运行这两个测试，依此类推。

可能有一个非常简单的解决方案。

Answer 1

pytest fixtures是适合您的解决方案。 fixture 的生命周期可能是单个测试、类、模块或整个测试 session 。

fixture management scales from simple unit to complex functional testing, allowing to parametrize fixtures and tests according to configuration and component options, or to re-use fixtures across function, class, module or whole test session scopes.

根据 Fixture availability paragraph ，您需要在类中或模块级别定义功能。

考虑使用模块范围的(注意，初始化只启动一次):

import pytest


@pytest.fixture(scope="module")
def heavy_context():
    # Use your LIST_OF_RANDOMIZED_PARAMS randomized parameters here
    # to initialize whatever you want.
    print("Slow fixture initialized")
    return ["I'm heavy"]


def test_1(heavy_context):
    print(f"\nUse of heavy context: {heavy_context[0]}")


def test_2(heavy_context):
    print(f"\nUse of heavy context: {heavy_context[0]}")

测试输出:

...
collecting ... collected 2 items

test_basic.py::test_1 Slow fixture initialized
PASSED                                             [ 50%]
Use of heavy context: I'm heavy

test_basic.py::test_2 PASSED                                             [100%]
Use of heavy context: I'm heavy

现在，如果您需要它是断言安全的(即使在测试失败时也释放资源)，请考虑以上下文管理器的方式创建 heavy_context(此处有更多详细信息:Fixture, Running multiple assert statements safely):

import pytest


@pytest.fixture(scope="module")
def heavy_context():

    print("Slow context initialized")
    obj = ["I'm heavy"]

    # It is mandatory to put deinitialiation into "finally" scope
    # otherwise in case of exception it won't be executed
    try:
        yield obj[0]
    finally:
        print("Slow context released")


def test_1(heavy_context):
    # Pay attention, that in fact heavy_context now
    # is what we initialized as 'obj' in heavy_context
    # function.
    print(f"\nUse of heavy context: {heavy_context}")


def test_2(heavy_context):
    print(f"\nUse of heavy context: {heavy_context}")

输出:

collecting ... collected 2 items

test_basic.py::test_1 Slow context initialized
PASSED                                             [ 50%]
Use of heavy context: I'm heavy

test_basic.py::test_2 PASSED                                             [100%]
Use of heavy context: I'm heavy
Slow context released


============================== 2 passed in 0.01s ===============================

Process finished with exit code 0