Question

I’m trying to write unit tests for a method that takes a String filename, then opens the file and reads from it. So, to test that method, I thought about writing a file, then calling my method. However, in the build farm, it is not possible to write files arbitrarily to disk. Is there a standard way to “simulate” having a real file in my unit test?

Answer 1

This is highly frowned upon:

The smallest amount of testable code. Often a single method/function,
sans the use of other methods or classes. Fast! Thousands of unit
tests can run in ten seconds or less! A unit test NEVER uses:

• a database
• an app server (or server of any kind)
• file/network I/O or file system;
• another application;
• the console (System.out, System.err, etc.)
• logging
• most other classes (exceptions include DTO’s, String, Integer, mocks and maybe a few others). "

Source

If you must read from a file, have a test file pre-generated that all unit tests read from. There is no need to write anything to disk.