例如，实际上如果不允许一个程序从文件系统进行读和写，很难测试它是否正确使用了该文件系统。

For example, it is difficult to test whether a program is making proper use of the filesystem without actually allowing it to read and write from the filesystem.

youdao

当一个测试失败或者得到意外的结果时，最好先去读一读日志文件。

Reading the log file is the best starting point for understanding a test that failed or produced surprising results.

youdao

但在单元测试中读和写文件会减缓测试，增加更多的复杂性(如创建临时目录和在使用后清除文件)。

But reading and writing files in unit tests slows tests and requires adding more complexity (like creating a temp directory and cleaning up files after use).

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