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We all know that there’s no limit in testing, if time is not a problem. So it’s a matter of trying to avoid customer-found bugs as more as possible by balancing the effort distribution in Unit Testing, Integration Testing and System Testing, given limited resource.

Pls let me be more specific. I suppose we won’t pursue a perfect coverage of either one of UT, IT or ST. Paying too much attention to only one of them and ignoring the others may not catch bugs effectively because they have differently focuses and perspectives. For example, UT validates internal logic; IT guarantees the stable interfaces/protocols among each other; ST is more from the user’s perspective, i.e. use case and scenario.

So generally all of them are necessary. We need to spend a reasonable degree of effort on each of them. For a specific project or situation, we still need to figure out what’s the best effort combination of them, with the minimum total testing effort spent.

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