the question is 'what is serious?' generally one can go about every piece of code with a mindset that if it fails the sky will fall, or on the other extreme 'let it fail' philosophy.

I like to take a mix of slow and fast approach. While some cases demand test-driven development, in other scenarios the test cases can follow the user demand. I like to build test coverage slowly depending on most used parts of the code. So they coverage catches up slowly but at the same time i am not spending time on test cases for things that don't get used at all.

This means, I would prefer releasing features in small batches and as the features start being used, I start improving the coverage. While this may not work for all the teams or environments, it is one approach to build early stage products. which I mostly do.