This goes better with a different way of testing - where you're not testing for specific outputs, but for things you want to be true of any implementation. E.g. suppose
Scramble(string) function should return some random-looking output, and suppose one of the requirements is that the scrambled output should be the same for the same input strings. You could write a test that has a prepared input string & checks for an expected output string, but then you'd have to change the test every time you change the scrambling algorithm. Instead, call Scramble twice and assert if the two outputs match.