python - 我想模拟打开一个现有的测试文件，对其应用一个函数进行测试，但不改变文件的实际内容

Question

我有一个更新 rpm 规范文件以供以后使用的功能。它具有三个参数：应用程序的名称、我们想要访问的版本以及规范文件在文件系统中的位置。

我似乎无法做的是拥有一个 tests/files/package_name.spec 文件并测试它是否正确地对其进行了版本化而不更改实际的规范文件。我不想更改实际的规范文件，因为它会使测试在第二次运行时变得无用。

我曾尝试查看模拟库和 mock_open 但似乎没有什么适合这种情况。

def test_update_spec_file():
    update_spec_file("package_name", "5.0.0", "files/package_name")
    with open("files/package_name.spec", "r") as f:
        contents = f.read()
        version_regex = re.compile("^.*define _software_version.*$")
        assert (
            re.search(version_regex, contents).group(0)
            == "%define _software_version 5.0.0"
        )

本质上，该update_spec_file函数的作用是使用 regex 找到该%define _software_version 5.0.0行并再次使用 regex 来插入新版本。

所以总而言之，是否有可能让文件存在，用某种带有其内容的模拟文件打开它，在其上运行函数，并断言它完成了它的工作而不实际修改文件系统中的文件？

要么在修改后重置文件。

这是更新规范文件的代码：

def update_spec_file(application, release_version, path_to_spec_file):
    """Update the spec file with the release version.

    Args:
        application (str): Name of the application.
        release_version (str): New version of application.
        path_to_spec_file (str, optional):
            path the the applications spec file we are modifying.
    """
    print(f"Updating spec file _software_version to {release_version}")

    try:
        with open(path_to_spec_file, "r") as spec_file:
            spec_contents = spec_file.readlines()
    except EnvironmentError:
        print(f"Unable to open spec file located at: {path_to_spec_file}")
        # raise the original exception again.
        raise

    # Find and replace software version in contents of spec file.
    version_regex = re.compile("%define _software_version.*?(?=(?:\\n)|$)")
    define_version = f"%define _software_version {release_version}"
    # Splice the new software version line into the existing file contents
    spec_contents[:] = [
        version_regex.sub(define_version, line) for line in spec_contents
    ]

    try:  # Open the file and write the new spliced contents
        with open(path_to_spec_file, "w") as f_spec_file:
            f_spec_file.writelines(spec_contents)
    except EnvironmentError:  # Catch spec file not found.
        print(f"Unable to open spec file located at: {path_to_spec_file}")
        # raise the original exception again.
        raise

编辑：

这是修改后的代码：

def test_update_spec_file():
    content = open("tests/files/package_name.spec").read()
    with patch(__name__ + ".open", create=True) as mock_open:
        mock_open.return_value.__enter__.return_value = StringIO(content)
        with open("tests/files/package_name.spec") as f:
            update_spec_file(
                "package_name", "5.0.0", "tests/files/package_name.spec"

我正在做的测试是cat在测试运行之前和测试运行cat之后的规范文件

代码的树结构：

release/
├── release_all_in_one
│   ├── changelog_utils.py
│   ├── confluence_email.py
│   ├── confluence_utils.py
│   ├── create_confluence_page.py
│   ├── __init__.py
│   ├── jira_utils.py
│   ├── parse_confluence.py
│   ├── parse_rm_objects.py
│   ├── release_all_in_one_openshift.py
│   ├── release_all_in_one.py
│   ├── tag_branch.py
│   ├── templates
│   │   ├── admin_package_template
│   │   ├── base_template
│   │   ├── cdn_package_template
│   │   ├── fe_package_template
│   │   ├── oddjob_package_template
│   │   ├── openshift_template
│   │   └── procedure.json
│   └── utils.py
├── setup.cfg
├── setup.py
└── tests
    ├── files
    │   └── package_name.spec
    ├── test_changelog.py
    ├── testing_utils.py
    └── test_utils.py

标签： pythonpython-3.xunit-testingtestingmocking

Answer 1

您可以patch使用该open函数返回一个上下文管理器，该管理器返回一个io.StringIO包含实际文件内容的对象：

from unittest.mock import patch
from io import StringIO
content = '123' # value for demo
# uncomment the line below to read actual file content
# content = open('files/package_name.spec').read()
with patch(__name__ + '.open', create=True) as mock_open:
    mock_open.return_value.__enter__.return_value = StringIO(content)
    with open('files/package_name.spec') as f:
        print(f.read())
        f.seek(0)
        f.write('abc')
        f.seek(0)
        print(f.read())

这输出：

123
abc

或者，您可以分配给open一个对象，以便覆盖同一模块中MagicMock的所有引用：open

from unittest.mock import MagicMock
from io import StringIO
content = '123' # value for demo
# uncomment the line below to read actual file content
# content = open('files/package_name.spec').read()
open = MagicMock()
open.return_value.__enter__.return_value = StringIO(content)
with open('files/package_name.spec') as f:
    print(f.read())
    f.seek(0)
    f.write('abc')
    f.seek(0)
    print(f.read())