Let\'s say there is a utility class that provides some common static methods use

Question

Let's say there is a utility class that provides some common static methods used everywhere in your code by many other classes.

How would you design your unit tests for the consumers of the utility so that their tests fail if any one of the utility tests do not pass? Can you do it or do you have to check it yourself whether the utility class tests are all green?

For example I have a message-splitter utility that is used (or rather its output) by a message-parser. I'd like to be sure that the message-splitter works correctly before the message-parser gets tested.

I have written tests for both of them but is there a way to link them and make one test depend on the result of some other test?

I couldn't find a suitable tag for this but I'm using Visual Studio's unit test engine.

Explanation / Answer

There is no point to making sure that every defect in your system trips exactly one test.

A test suite has one job: verifying that there are no known defects. If there is a defect, it doesn't matter if one test fails or 10. If you get used to your test suite failing, if you try to gauge how "bad" your program is by counting the failing tests, you're not using regression testing the right way. The test suite should pass all tests before you publish code.

The only valid reason for skipping tests is if they test incomplete functionality and take an inordinate amount of time that you could put to better use while implementing the thing they're supposed to test. (That is only an issue if you don't practice strict test-driven development, but that's a valid choice, after all.)

Otherwise, don't bother trying to make your test suite into an indicator telling you precisely what's wrong. It will never be exact, and it's not supposed to be. It's supposed to protect you from making the same mistake twice, that's all.

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