Re^3: Delete all hash keys except for n of them

Well, presumably, the data has to enter the program from somewhere. That is the place you want to modify what your data is. Instead of modifying the script that does the processing, modify the data that the script will process. This also has the side-benefit of helping you understand your data more. Maybe, it's too complicated or too simple.

This is, in the general, called "Creating Your Test Environment", and it should be one of the first things a developer does when working on an application. For, if you cannot verify that your change(s) do what they should, how do you know you did the right thing?

As for testing very specific parts of a program, you may want to pull those parts out and test them independently. You can always use MockObjects to give it the scaffolding it needs. If you cannot do this step in a simple manner, then that is a "Red Flag"™ that should be dealt with through refactoring.

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