在不同的进程中运行 py.test 测试 [英] Run py.test test in different process

问题描述

我正在尝试测试 tensorflow 程序.我正在使用参数化的 py.test 夹具设置 tensorflow 会话:

I'm trying to test tensorflow program. I'm setting up tensorflow session using parametrized py.test fixture:

@pytest.fixture(scope="session", params=configuration)
def session(request):
    if request.param == 'tensorflow':
        return tf.Session()
    elif request.param == 'tensorflow-eager':
        tfe.enable_eager_execution()
        return tf.Session()
    elif ...

Tensorflow 具有全局状态，因此多次测试启动可能会污染它.例如，在启用 Eager Execution 后无法禁用它.有没有办法指示 py.test 为每个测试创建一个新进程?或者除了使用参数化夹具之外的另一种为测试配置环境的方法?示例用法:

Tensorflow has global state, thus several test launches can pollute it. For example there is no way to disable eager execution after it has been enabled. Is there a way to instruct py.test to create a new process for each test? Or another way to configure environment for the test besides using parametrized fixture? Example usage:

@pytest.mark.parametrize("bias_type", ['variable', 'ndarray', 'list', 'tuple'])
@pytest.mark.parametrize("kernel_type", ['variable', 'ndarray', 'list', 'tuple'])
@pytest.mark.parametrize("input_type", ['variable', 'ndarray', 'list', 'tuple'])
def test_convolution(session, input_type, kernel_type, bias_type):
    ...

推荐答案

正如评论中所建议的，使用 pytest-xdist 将是解决方案.该插件专为并行或分布式执行测试而设计(甚至可以进行多平台执行)，但非常适合满足您在单独进程中运行每个测试的要求 - 您可以使用 --分叉参数.

As suggested in the comments, using pytest-xdist will be the solution. The plugin is designed for parallel or distributed execution of tests (even a multi-platform execution is possible), but is well suited to serve your request of running each test in a separate process - you can achieve this with the --forked argument.

--forked 参数在 Windows 上不起作用，因为 Windows 不支持 fork-exec 模型并且不提供 fork() 的任何替代品.

--forked argument will not work on Windows, because Windows doesn't support the fork-exec model and doesn't ship any replacement for fork().

让我们定义一个fixture，它会在运行每个测试之前尝试开启急切执行:

Let's define a fixture that will attempt to turn the eager execution on before running each test:

from tensorflow.contrib.eager.python import tfe

import pytest


@pytest.fixture(scope='function', autouse=True)
def eager(request):
    tfe.enable_eager_execution()

这个夹具显然会失败所有测试，但第一个因为急切执行只能被打开一次.通过一些虚拟测试:

This fixture will obviously fail all tests but the first one since the eager execution can be turned only once. With some dummy tests:

def test_spam():
    assert True

def test_eggs():
    assert True

def test_bacon():
    assert True

按预期运行普通 pytest 失败:

Running plain pytest fails as expected:

$ pytest -v
============================== test session starts ================================
platform darwin -- Python 3.6.3, pytest-3.3.1, py-1.5.2, pluggy-0.6.0 -- /Users/hoefling/.virtualenvs/stackoverflow/bin/python3.6
cachedir: .cache
rootdir: /Users/hoefling/projects/private/stackoverflow/so-48234032, inifile:
plugins: forked-0.2, mock-1.6.3, hypothesis-3.44.4
collected 3 items

test_spam.py::test_spam PASSED                                                [ 33%]
test_spam.py::test_eggs ERROR                                                 [ 66%]
test_spam.py::test_bacon ERROR                                                [100%]

...
E       ValueError: Do not call tfe.enable_eager_execution more than once in the
same process. Note eager-mode methods such as tfe.run() also call 
tfe.enable_eager_execution.
...

现在安装pytest-xdist:

$ pip install pytest-xdist

并重新运行测试:

$ pytest -v --forked
============================== test session starts ================================
platform darwin -- Python 3.6.3, pytest-3.3.1, py-1.5.2, pluggy-0.6.0 -- /Users/hoefling/.virtualenvs/stackoverflow/bin/python3.6
cachedir: .cache
rootdir: /Users/hoefling/projects/private/stackoverflow/so-48234032, inifile:
plugins: forked-0.2, xdist-1.22.0, mock-1.6.3, hypothesis-3.44.4
collected 3 items

test_spam.py::test_spam PASSED                                                [ 33%]
test_spam.py::test_eggs PASSED                                                [ 66%]
test_spam.py::test_bacon PASSED                                               [100%]

============================= 3 passed in 6.09 seconds ============================

测试仍然按顺序运行，但每个测试都在自己的子进程中，因此它们都不会失败.

The tests still run sequentially, but each one in an own subprocess, so none of them fails.

现在您可以开始尝试并行执行，例如

Now you can start experimenting with parallel execution, e.g.

$ pytest -v --forked --numprocesses=auto

等等.请参阅插件文档了解更多信息和更多使用示例.

etc. Refer to plugin docs for more info and more usage examples.

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