I would mock/hook/monkey patch/whatever the functions to get the current time/elapsed time, simulate a period of time (a day/week/month/year/whatever), make sure the function to download the file is called the correct amount of times. That would probably catch this bug.
Although, after such a fuck up, I would be tempted to make a pre-release check that tests the compiled binary, not any unit test or whatever. Use LD_PRELOAD to hook the system timing functions(a quick google shows that libfaketime[0] exists, but I've never used it), launch the real program and speed up time to make sure it doesn't try to download more than once.
Although, after such a fuck up, I would be tempted to make a pre-release check that tests the compiled binary, not any unit test or whatever. Use LD_PRELOAD to hook the system timing functions(a quick google shows that libfaketime[0] exists, but I've never used it), launch the real program and speed up time to make sure it doesn't try to download more than once.
[0] https://github.com/wolfcw/libfaketime