I'm curious to know thoughts on writing tests that specify the behavior of a method when its inputs are incorrect. ?Is this a common practice. ?How about parameter validation in this case? ?Having some healthy debate on it and wanted to get other insight.

The context for this in a class/methods that are used within an internal application - this is not an API that will be publicly exposed to external consumers.

Thanks.
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It does seem to me that even if you develop 'inside out' you will sometimes need to work 'outside in', for example if you are using a mock, or if you apply refactorings that extract classes or methods.