如何使用 mocking/patching 更改 class 方法中的本地目录变量以避免将测试输出文件写入其中？

Question

我有一个如下所示的对象，其中包含一个 to_json 方法，我想为其编写测试。

import networkx as nx

class Example:
    def __init__(self, graph):
        self.graph = graph

    def to_json(self):
        data = nx.readwrite.node_link_data(self.graph)
        filepath = os.path.join('~/.cache/product', 'some_file_name.txt')
        with open(filepath, "w") as outfile:
            json.dump(data, outfile)
        return filepath

运行 to_json 的单元测试时，我不想将输出文件写入 ~/.cache/product 目录，而是 /tmp/product 目录。我如何使用 mocking/patching?

实现此目的

我当前的测试设置类似于：

def test_example_to_json():
    ex = Example(graph={}) # Some graph
    filepath = ex.to_json() # This is the problematic step since the file is being written to ~/.cache/product
    with open(filepath, "r") as infile:
        assert json.load(infile) == {}

如有任何建议，我们将不胜感激。

Answer 1

无法更改 filepath 变量然后让函数通过 mocking/patching 继续进行其余计算。

此处对我有用的一个解决方案如下：我定义了一个名为 CACHE_DIR 的环境变量，并使用它来获取缓存目录。 Monkeypatch 允许您使用 monkeypatch.setenv("CACHE_DIR", "/tmp/product").

import networkx as nx


class Example:
    def __init__(self, graph):
        self.graph = graph

    def to_json(self):
        data = nx.readwrite.node_link_data(self.graph)
        filepath = os.path.join(os.getenv('CACHE_DIR'), 'some_file_name.txt')
        with open(filepath, "w") as outfile:
            json.dump(data, outfile)
        return filepath

使用以下单元测试：

import pytest


def test_example_to_json(monkeypatch):
    ex = Example(graph={})

    monkeypatch.setenv("CACHE_DIR", "/tmp/product")
    filepath = ex.to_json() 
    with open(filepath, "r") as infile:
        assert json.load(infile) == {}

如何使用 mocking/patching 更改 class 方法中的本地目录变量以避免将测试输出文件写入其中？

How can I use mocking/patching for changing the local directory variable inside a class method to avoid writing test output files into it?

unit-testing

monkeypatching

mocking